Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild

[deliverable/linux.git] / include / linux / jbd2.h

/*
 * linux/include/linux/jbd2.h
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>
 *
 * Copyright 1998-2000 Red Hat, Inc --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Definitions for transaction data structures for the buffer cache
 * filesystem journaling support.
 */

#ifndef _LINUX_JBD2_H
#define _LINUX_JBD2_H

/* Allow this file to be included directly into e2fsprogs */
#ifndef __KERNEL__
#include "jfs_compat.h"
#define JBD2_DEBUG
#else

#include <linux/types.h>
#include <linux/buffer_head.h>
#include <linux/journal-head.h>
#include <linux/stddef.h>
#include <linux/mutex.h>
#include <linux/timer.h>
#include <linux/slab.h>
#include <linux/bit_spinlock.h>
#include <crypto/hash.h>
#endif

#define journal_oom_retry 1

/*
 * Define JBD2_PARANIOD_IOFAIL to cause a kernel BUG() if ext4 finds
 * certain classes of error which can occur due to failed IOs.  Under
 * normal use we want ext4 to continue after such errors, because
 * hardware _can_ fail, but for debugging purposes when running tests on
 * known-good hardware we may want to trap these errors.
 */
#undef JBD2_PARANOID_IOFAIL

/*
 * The default maximum commit age, in seconds.
 */
#define JBD2_DEFAULT_MAX_COMMIT_AGE 5

#ifdef CONFIG_JBD2_DEBUG
/*
 * Define JBD2_EXPENSIVE_CHECKING to enable more expensive internal
 * consistency checks.  By default we don't do this unless
 * CONFIG_JBD2_DEBUG is on.
 */
#define JBD2_EXPENSIVE_CHECKING
extern ushort jbd2_journal_enable_debug;
void __jbd2_debug(int level, const char *file, const char *func,
                  unsigned int line, const char *fmt, ...);

#define jbd_debug(n, fmt, a...) \
        __jbd2_debug((n), __FILE__, __func__, __LINE__, (fmt), ##a)
#else
#define jbd_debug(n, fmt, a...)    /**/
#endif

extern void *jbd2_alloc(size_t size, gfp_t flags);
extern void jbd2_free(void *ptr, size_t size);

#define JBD2_MIN_JOURNAL_BLOCKS 1024

#ifdef __KERNEL__

/**
 * typedef handle_t - The handle_t type represents a single atomic update being performed by some process.
 *
 * All filesystem modifications made by the process go
 * through this handle.  Recursive operations (such as quota operations)
 * are gathered into a single update.
 *
 * The buffer credits field is used to account for journaled buffers
 * being modified by the running process.  To ensure that there is
 * enough log space for all outstanding operations, we need to limit the
 * number of outstanding buffers possible at any time.  When the
 * operation completes, any buffer credits not used are credited back to
 * the transaction, so that at all times we know how many buffers the
 * outstanding updates on a transaction might possibly touch.
 *
 * This is an opaque datatype.
 **/
typedef struct jbd2_journal_handle handle_t;    /* Atomic operation type */


/**
 * typedef journal_t - The journal_t maintains all of the journaling state information for a single filesystem.
 *
 * journal_t is linked to from the fs superblock structure.
 *
 * We use the journal_t to keep track of all outstanding transaction
 * activity on the filesystem, and to manage the state of the log
 * writing process.
 *
 * This is an opaque datatype.
 **/
typedef struct journal_s        journal_t;      /* Journal control structure */
#endif

/*
 * Internal structures used by the logging mechanism:
 */

#define JBD2_MAGIC_NUMBER 0xc03b3998U /* The first 4 bytes of /dev/random! */

/*
 * On-disk structures
 */

/*
 * Descriptor block types:
 */

#define JBD2_DESCRIPTOR_BLOCK   1
#define JBD2_COMMIT_BLOCK       2
#define JBD2_SUPERBLOCK_V1      3
#define JBD2_SUPERBLOCK_V2      4
#define JBD2_REVOKE_BLOCK       5

/*
 * Standard header for all descriptor blocks:
 */
typedef struct journal_header_s
{
        __be32          h_magic;
        __be32          h_blocktype;
        __be32          h_sequence;
} journal_header_t;

/*
 * Checksum types.
 */
#define JBD2_CRC32_CHKSUM   1
#define JBD2_MD5_CHKSUM     2
#define JBD2_SHA1_CHKSUM    3
#define JBD2_CRC32C_CHKSUM  4

#define JBD2_CRC32_CHKSUM_SIZE 4

#define JBD2_CHECKSUM_BYTES (32 / sizeof(u32))
/*
 * Commit block header for storing transactional checksums:
 *
 * NOTE: If FEATURE_COMPAT_CHECKSUM (checksum v1) is set, the h_chksum*
 * fields are used to store a checksum of the descriptor and data blocks.
 *
 * If FEATURE_INCOMPAT_CSUM_V2 (checksum v2) is set, then the h_chksum
 * field is used to store crc32c(uuid+commit_block).  Each journal metadata
 * block gets its own checksum, and data block checksums are stored in
 * journal_block_tag (in the descriptor).  The other h_chksum* fields are
 * not used.
 *
 * If FEATURE_INCOMPAT_CSUM_V3 is set, the descriptor block uses
 * journal_block_tag3_t to store a full 32-bit checksum.  Everything else
 * is the same as v2.
 *
 * Checksum v1, v2, and v3 are mutually exclusive features.
 */
struct commit_header {
        __be32          h_magic;
        __be32          h_blocktype;
        __be32          h_sequence;
        unsigned char   h_chksum_type;
        unsigned char   h_chksum_size;
        unsigned char   h_padding[2];
        __be32          h_chksum[JBD2_CHECKSUM_BYTES];
        __be64          h_commit_sec;
        __be32          h_commit_nsec;
};

/*
 * The block tag: used to describe a single buffer in the journal.
 * t_blocknr_high is only used if INCOMPAT_64BIT is set, so this
 * raw struct shouldn't be used for pointer math or sizeof() - use
 * journal_tag_bytes(journal) instead to compute this.
 */
typedef struct journal_block_tag3_s
{
        __be32          t_blocknr;      /* The on-disk block number */
        __be32          t_flags;        /* See below */
        __be32          t_blocknr_high; /* most-significant high 32bits. */
        __be32          t_checksum;     /* crc32c(uuid+seq+block) */
} journal_block_tag3_t;

typedef struct journal_block_tag_s
{
        __be32          t_blocknr;      /* The on-disk block number */
        __be16          t_checksum;     /* truncated crc32c(uuid+seq+block) */
        __be16          t_flags;        /* See below */
        __be32          t_blocknr_high; /* most-significant high 32bits. */
} journal_block_tag_t;

/* Tail of descriptor or revoke block, for checksumming */
struct jbd2_journal_block_tail {
        __be32          t_checksum;     /* crc32c(uuid+descr_block) */
};

/*
 * The revoke descriptor: used on disk to describe a series of blocks to
 * be revoked from the log
 */
typedef struct jbd2_journal_revoke_header_s
{
        journal_header_t r_header;
        __be32           r_count;       /* Count of bytes used in the block */
} jbd2_journal_revoke_header_t;

/* Definitions for the journal tag flags word: */
#define JBD2_FLAG_ESCAPE                1       /* on-disk block is escaped */
#define JBD2_FLAG_SAME_UUID     2       /* block has same uuid as previous */
#define JBD2_FLAG_DELETED       4       /* block deleted by this transaction */
#define JBD2_FLAG_LAST_TAG      8       /* last tag in this descriptor block */


/*
 * The journal superblock.  All fields are in big-endian byte order.
 */
typedef struct journal_superblock_s
{
/* 0x0000 */
        journal_header_t s_header;

/* 0x000C */
        /* Static information describing the journal */
        __be32  s_blocksize;            /* journal device blocksize */
        __be32  s_maxlen;               /* total blocks in journal file */
        __be32  s_first;                /* first block of log information */

/* 0x0018 */
        /* Dynamic information describing the current state of the log */
        __be32  s_sequence;             /* first commit ID expected in log */
        __be32  s_start;                /* blocknr of start of log */

/* 0x0020 */
        /* Error value, as set by jbd2_journal_abort(). */
        __be32  s_errno;

/* 0x0024 */
        /* Remaining fields are only valid in a version-2 superblock */
        __be32  s_feature_compat;       /* compatible feature set */
        __be32  s_feature_incompat;     /* incompatible feature set */
        __be32  s_feature_ro_compat;    /* readonly-compatible feature set */
/* 0x0030 */
        __u8    s_uuid[16];             /* 128-bit uuid for journal */

/* 0x0040 */
        __be32  s_nr_users;             /* Nr of filesystems sharing log */

        __be32  s_dynsuper;             /* Blocknr of dynamic superblock copy*/

/* 0x0048 */
        __be32  s_max_transaction;      /* Limit of journal blocks per trans.*/
        __be32  s_max_trans_data;       /* Limit of data blocks per trans. */

/* 0x0050 */
        __u8    s_checksum_type;        /* checksum type */
        __u8    s_padding2[3];
        __u32   s_padding[42];
        __be32  s_checksum;             /* crc32c(superblock) */

/* 0x0100 */
        __u8    s_users[16*48];         /* ids of all fs'es sharing the log */
/* 0x0400 */
} journal_superblock_t;

/* Use the jbd2_{has,set,clear}_feature_* helpers; these will be removed */
#define JBD2_HAS_COMPAT_FEATURE(j,mask)                                 \
        ((j)->j_format_version >= 2 &&                                  \
         ((j)->j_superblock->s_feature_compat & cpu_to_be32((mask))))
#define JBD2_HAS_RO_COMPAT_FEATURE(j,mask)                              \
        ((j)->j_format_version >= 2 &&                                  \
         ((j)->j_superblock->s_feature_ro_compat & cpu_to_be32((mask))))
#define JBD2_HAS_INCOMPAT_FEATURE(j,mask)                               \
        ((j)->j_format_version >= 2 &&                                  \
         ((j)->j_superblock->s_feature_incompat & cpu_to_be32((mask))))

#define JBD2_FEATURE_COMPAT_CHECKSUM            0x00000001

#define JBD2_FEATURE_INCOMPAT_REVOKE            0x00000001
#define JBD2_FEATURE_INCOMPAT_64BIT             0x00000002
#define JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT      0x00000004
#define JBD2_FEATURE_INCOMPAT_CSUM_V2           0x00000008
#define JBD2_FEATURE_INCOMPAT_CSUM_V3           0x00000010

/* See "journal feature predicate functions" below */

/* Features known to this kernel version: */
#define JBD2_KNOWN_COMPAT_FEATURES      JBD2_FEATURE_COMPAT_CHECKSUM
#define JBD2_KNOWN_ROCOMPAT_FEATURES    0
#define JBD2_KNOWN_INCOMPAT_FEATURES    (JBD2_FEATURE_INCOMPAT_REVOKE | \
                                        JBD2_FEATURE_INCOMPAT_64BIT | \
                                        JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT | \
                                        JBD2_FEATURE_INCOMPAT_CSUM_V2 | \
                                        JBD2_FEATURE_INCOMPAT_CSUM_V3)

#ifdef __KERNEL__

#include <linux/fs.h>
#include <linux/sched.h>

enum jbd_state_bits {
        BH_JBD                  /* Has an attached ext3 journal_head */
          = BH_PrivateStart,
        BH_JWrite,              /* Being written to log (@@@ DEBUGGING) */
        BH_Freed,               /* Has been freed (truncated) */
        BH_Revoked,             /* Has been revoked from the log */
        BH_RevokeValid,         /* Revoked flag is valid */
        BH_JBDDirty,            /* Is dirty but journaled */
        BH_State,               /* Pins most journal_head state */
        BH_JournalHead,         /* Pins bh->b_private and jh->b_bh */
        BH_Shadow,              /* IO on shadow buffer is running */
        BH_Verified,            /* Metadata block has been verified ok */
        BH_JBDPrivateStart,     /* First bit available for private use by FS */
};

BUFFER_FNS(JBD, jbd)
BUFFER_FNS(JWrite, jwrite)
BUFFER_FNS(JBDDirty, jbddirty)
TAS_BUFFER_FNS(JBDDirty, jbddirty)
BUFFER_FNS(Revoked, revoked)
TAS_BUFFER_FNS(Revoked, revoked)
BUFFER_FNS(RevokeValid, revokevalid)
TAS_BUFFER_FNS(RevokeValid, revokevalid)
BUFFER_FNS(Freed, freed)
BUFFER_FNS(Shadow, shadow)
BUFFER_FNS(Verified, verified)

static inline struct buffer_head *jh2bh(struct journal_head *jh)
{
        return jh->b_bh;
}

static inline struct journal_head *bh2jh(struct buffer_head *bh)
{
        return bh->b_private;
}

static inline void jbd_lock_bh_state(struct buffer_head *bh)
{
        bit_spin_lock(BH_State, &bh->b_state);
}

static inline int jbd_trylock_bh_state(struct buffer_head *bh)
{
        return bit_spin_trylock(BH_State, &bh->b_state);
}

static inline int jbd_is_locked_bh_state(struct buffer_head *bh)
{
        return bit_spin_is_locked(BH_State, &bh->b_state);
}

static inline void jbd_unlock_bh_state(struct buffer_head *bh)
{
        bit_spin_unlock(BH_State, &bh->b_state);
}

static inline void jbd_lock_bh_journal_head(struct buffer_head *bh)
{
        bit_spin_lock(BH_JournalHead, &bh->b_state);
}

static inline void jbd_unlock_bh_journal_head(struct buffer_head *bh)
{
        bit_spin_unlock(BH_JournalHead, &bh->b_state);
}

#define J_ASSERT(assert)        BUG_ON(!(assert))

#define J_ASSERT_BH(bh, expr)   J_ASSERT(expr)
#define J_ASSERT_JH(jh, expr)   J_ASSERT(expr)

#if defined(JBD2_PARANOID_IOFAIL)
#define J_EXPECT(expr, why...)          J_ASSERT(expr)
#define J_EXPECT_BH(bh, expr, why...)   J_ASSERT_BH(bh, expr)
#define J_EXPECT_JH(jh, expr, why...)   J_ASSERT_JH(jh, expr)
#else
#define __journal_expect(expr, why...)                                       \
        ({                                                                   \
                int val = (expr);                                            \
                if (!val) {                                                  \
                        printk(KERN_ERR                                      \
                               "JBD2 unexpected failure: %s: %s;\n",         \
                               __func__, #expr);                             \
                        printk(KERN_ERR why "\n");                           \
                }                                                            \
                val;                                                         \
        })
#define J_EXPECT(expr, why...)          __journal_expect(expr, ## why)
#define J_EXPECT_BH(bh, expr, why...)   __journal_expect(expr, ## why)
#define J_EXPECT_JH(jh, expr, why...)   __journal_expect(expr, ## why)
#endif

/* Flags in jbd_inode->i_flags */
#define __JI_COMMIT_RUNNING 0
/* Commit of the inode data in progress. We use this flag to protect us from
 * concurrent deletion of inode. We cannot use reference to inode for this
 * since we cannot afford doing last iput() on behalf of kjournald
 */
#define JI_COMMIT_RUNNING (1 << __JI_COMMIT_RUNNING)

/**
 * struct jbd_inode is the structure linking inodes in ordered mode
 *   present in a transaction so that we can sync them during commit.
 */
struct jbd2_inode {
        /* Which transaction does this inode belong to? Either the running
         * transaction or the committing one. [j_list_lock] */
        transaction_t *i_transaction;

        /* Pointer to the running transaction modifying inode's data in case
         * there is already a committing transaction touching it. [j_list_lock] */
        transaction_t *i_next_transaction;

        /* List of inodes in the i_transaction [j_list_lock] */
        struct list_head i_list;

        /* VFS inode this inode belongs to [constant during the lifetime
         * of the structure] */
        struct inode *i_vfs_inode;

        /* Flags of inode [j_list_lock] */
        unsigned long i_flags;
};

struct jbd2_revoke_table_s;

/**
 * struct handle_s - The handle_s type is the concrete type associated with
 *     handle_t.
 * @h_transaction: Which compound transaction is this update a part of?
 * @h_buffer_credits: Number of remaining buffers we are allowed to dirty.
 * @h_ref: Reference count on this handle
 * @h_err: Field for caller's use to track errors through large fs operations
 * @h_sync: flag for sync-on-close
 * @h_jdata: flag to force data journaling
 * @h_aborted: flag indicating fatal error on handle
 **/

/* Docbook can't yet cope with the bit fields, but will leave the documentation
 * in so it can be fixed later.
 */

struct jbd2_journal_handle
{
        union {
                /* Which compound transaction is this update a part of? */
                transaction_t   *h_transaction;
                /* Which journal handle belongs to - used iff h_reserved set */
                journal_t       *h_journal;
        };

        /* Handle reserved for finishing the logical operation */
        handle_t                *h_rsv_handle;

        /* Number of remaining buffers we are allowed to dirty: */
        int                     h_buffer_credits;

        /* Reference count on this handle */
        int                     h_ref;

        /* Field for caller's use to track errors through large fs */
        /* operations */
        int                     h_err;

        /* Flags [no locking] */
        unsigned int    h_sync:         1;      /* sync-on-close */
        unsigned int    h_jdata:        1;      /* force data journaling */
        unsigned int    h_reserved:     1;      /* handle with reserved credits */
        unsigned int    h_aborted:      1;      /* fatal error on handle */
        unsigned int    h_type:         8;      /* for handle statistics */
        unsigned int    h_line_no:      16;     /* for handle statistics */

        unsigned long           h_start_jiffies;
        unsigned int            h_requested_credits;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lockdep_map      h_lockdep_map;
#endif
};


/*
 * Some stats for checkpoint phase
 */
struct transaction_chp_stats_s {
        unsigned long           cs_chp_time;
        __u32                   cs_forced_to_close;
        __u32                   cs_written;
        __u32                   cs_dropped;
};

/* The transaction_t type is the guts of the journaling mechanism.  It
 * tracks a compound transaction through its various states:
 *
 * RUNNING:     accepting new updates
 * LOCKED:      Updates still running but we don't accept new ones
 * RUNDOWN:     Updates are tidying up but have finished requesting
 *              new buffers to modify (state not used for now)
 * FLUSH:       All updates complete, but we are still writing to disk
 * COMMIT:      All data on disk, writing commit record
 * FINISHED:    We still have to keep the transaction for checkpointing.
 *
 * The transaction keeps track of all of the buffers modified by a
 * running transaction, and all of the buffers committed but not yet
 * flushed to home for finished transactions.
 */

/*
 * Lock ranking:
 *
 *    j_list_lock
 *      ->jbd_lock_bh_journal_head()    (This is "innermost")
 *
 *    j_state_lock
 *    ->jbd_lock_bh_state()
 *
 *    jbd_lock_bh_state()
 *    ->j_list_lock
 *
 *    j_state_lock
 *    ->t_handle_lock
 *
 *    j_state_lock
 *    ->j_list_lock                     (journal_unmap_buffer)
 *
 */

struct transaction_s
{
        /* Pointer to the journal for this transaction. [no locking] */
        journal_t               *t_journal;

        /* Sequence number for this transaction [no locking] */
        tid_t                   t_tid;

        /*
         * Transaction's current state
         * [no locking - only kjournald2 alters this]
         * [j_list_lock] guards transition of a transaction into T_FINISHED
         * state and subsequent call of __jbd2_journal_drop_transaction()
         * FIXME: needs barriers
         * KLUDGE: [use j_state_lock]
         */
        enum {
                T_RUNNING,
                T_LOCKED,
                T_FLUSH,
                T_COMMIT,
                T_COMMIT_DFLUSH,
                T_COMMIT_JFLUSH,
                T_COMMIT_CALLBACK,
                T_FINISHED
        }                       t_state;

        /*
         * Where in the log does this transaction's commit start? [no locking]
         */
        unsigned long           t_log_start;

        /* Number of buffers on the t_buffers list [j_list_lock] */
        int                     t_nr_buffers;

        /*
         * Doubly-linked circular list of all buffers reserved but not yet
         * modified by this transaction [j_list_lock]
         */
        struct journal_head     *t_reserved_list;

        /*
         * Doubly-linked circular list of all metadata buffers owned by this
         * transaction [j_list_lock]
         */
        struct journal_head     *t_buffers;

        /*
         * Doubly-linked circular list of all forget buffers (superseded
         * buffers which we can un-checkpoint once this transaction commits)
         * [j_list_lock]
         */
        struct journal_head     *t_forget;

        /*
         * Doubly-linked circular list of all buffers still to be flushed before
         * this transaction can be checkpointed. [j_list_lock]
         */
        struct journal_head     *t_checkpoint_list;

        /*
         * Doubly-linked circular list of all buffers submitted for IO while
         * checkpointing. [j_list_lock]
         */
        struct journal_head     *t_checkpoint_io_list;

        /*
         * Doubly-linked circular list of metadata buffers being shadowed by log
         * IO.  The IO buffers on the iobuf list and the shadow buffers on this
         * list match each other one for one at all times. [j_list_lock]
         */
        struct journal_head     *t_shadow_list;

        /*
         * List of inodes whose data we've modified in data=ordered mode.
         * [j_list_lock]
         */
        struct list_head        t_inode_list;

        /*
         * Protects info related to handles
         */
        spinlock_t              t_handle_lock;

        /*
         * Longest time some handle had to wait for running transaction
         */
        unsigned long           t_max_wait;

        /*
         * When transaction started
         */
        unsigned long           t_start;

        /*
         * When commit was requested
         */
        unsigned long           t_requested;

        /*
         * Checkpointing stats [j_checkpoint_sem]
         */
        struct transaction_chp_stats_s t_chp_stats;

        /*
         * Number of outstanding updates running on this transaction
         * [t_handle_lock]
         */
        atomic_t                t_updates;

        /*
         * Number of buffers reserved for use by all handles in this transaction
         * handle but not yet modified. [t_handle_lock]
         */
        atomic_t                t_outstanding_credits;

        /*
         * Forward and backward links for the circular list of all transactions
         * awaiting checkpoint. [j_list_lock]
         */
        transaction_t           *t_cpnext, *t_cpprev;

        /*
         * When will the transaction expire (become due for commit), in jiffies?
         * [no locking]
         */
        unsigned long           t_expires;

        /*
         * When this transaction started, in nanoseconds [no locking]
         */
        ktime_t                 t_start_time;

        /*
         * How many handles used this transaction? [t_handle_lock]
         */
        atomic_t                t_handle_count;

        /*
         * This transaction is being forced and some process is
         * waiting for it to finish.
         */
        unsigned int t_synchronous_commit:1;

        /* Disk flush needs to be sent to fs partition [no locking] */
        int                     t_need_data_flush;

        /*
         * For use by the filesystem to store fs-specific data
         * structures associated with the transaction
         */
        struct list_head        t_private_list;
};

struct transaction_run_stats_s {
        unsigned long           rs_wait;
        unsigned long           rs_request_delay;
        unsigned long           rs_running;
        unsigned long           rs_locked;
        unsigned long           rs_flushing;
        unsigned long           rs_logging;

        __u32                   rs_handle_count;
        __u32                   rs_blocks;
        __u32                   rs_blocks_logged;
};

struct transaction_stats_s {
        unsigned long           ts_tid;
        unsigned long           ts_requested;
        struct transaction_run_stats_s run;
};

static inline unsigned long
jbd2_time_diff(unsigned long start, unsigned long end)
{
        if (end >= start)
                return end - start;

        return end + (MAX_JIFFY_OFFSET - start);
}

#define JBD2_NR_BATCH   64

/**
 * struct journal_s - The journal_s type is the concrete type associated with
 *     journal_t.
 * @j_flags:  General journaling state flags
 * @j_errno:  Is there an outstanding uncleared error on the journal (from a
 *     prior abort)?
 * @j_sb_buffer: First part of superblock buffer
 * @j_superblock: Second part of superblock buffer
 * @j_format_version: Version of the superblock format
 * @j_state_lock: Protect the various scalars in the journal
 * @j_barrier_count:  Number of processes waiting to create a barrier lock
 * @j_barrier: The barrier lock itself
 * @j_running_transaction: The current running transaction..
 * @j_committing_transaction: the transaction we are pushing to disk
 * @j_checkpoint_transactions: a linked circular list of all transactions
 *  waiting for checkpointing
 * @j_wait_transaction_locked: Wait queue for waiting for a locked transaction
 *  to start committing, or for a barrier lock to be released
 * @j_wait_done_commit: Wait queue for waiting for commit to complete
 * @j_wait_commit: Wait queue to trigger commit
 * @j_wait_updates: Wait queue to wait for updates to complete
 * @j_wait_reserved: Wait queue to wait for reserved buffer credits to drop
 * @j_checkpoint_mutex: Mutex for locking against concurrent checkpoints
 * @j_head: Journal head - identifies the first unused block in the journal
 * @j_tail: Journal tail - identifies the oldest still-used block in the
 *  journal.
 * @j_free: Journal free - how many free blocks are there in the journal?
 * @j_first: The block number of the first usable block
 * @j_last: The block number one beyond the last usable block
 * @j_dev: Device where we store the journal
 * @j_blocksize: blocksize for the location where we store the journal.
 * @j_blk_offset: starting block offset for into the device where we store the
 *     journal
 * @j_fs_dev: Device which holds the client fs.  For internal journal this will
 *     be equal to j_dev
 * @j_reserved_credits: Number of buffers reserved from the running transaction
 * @j_maxlen: Total maximum capacity of the journal region on disk.
 * @j_list_lock: Protects the buffer lists and internal buffer state.
 * @j_inode: Optional inode where we store the journal.  If present, all journal
 *     block numbers are mapped into this inode via bmap().
 * @j_tail_sequence:  Sequence number of the oldest transaction in the log
 * @j_transaction_sequence: Sequence number of the next transaction to grant
 * @j_commit_sequence: Sequence number of the most recently committed
 *  transaction
 * @j_commit_request: Sequence number of the most recent transaction wanting
 *     commit
 * @j_uuid: Uuid of client object.
 * @j_task: Pointer to the current commit thread for this journal
 * @j_max_transaction_buffers:  Maximum number of metadata buffers to allow in a
 *     single compound commit transaction
 * @j_commit_interval: What is the maximum transaction lifetime before we begin
 *  a commit?
 * @j_commit_timer:  The timer used to wakeup the commit thread
 * @j_revoke_lock: Protect the revoke table
 * @j_revoke: The revoke table - maintains the list of revoked blocks in the
 *     current transaction.
 * @j_revoke_table: alternate revoke tables for j_revoke
 * @j_wbuf: array of buffer_heads for jbd2_journal_commit_transaction
 * @j_wbufsize: maximum number of buffer_heads allowed in j_wbuf, the
 *      number that will fit in j_blocksize
 * @j_last_sync_writer: most recent pid which did a synchronous write
 * @j_history: Buffer storing the transactions statistics history
 * @j_history_max: Maximum number of transactions in the statistics history
 * @j_history_cur: Current number of transactions in the statistics history
 * @j_history_lock: Protect the transactions statistics history
 * @j_proc_entry: procfs entry for the jbd statistics directory
 * @j_stats: Overall statistics
 * @j_private: An opaque pointer to fs-private information.
 */

struct journal_s
{
        /* General journaling state flags [j_state_lock] */
        unsigned long           j_flags;

        /*
         * Is there an outstanding uncleared error on the journal (from a prior
         * abort)? [j_state_lock]
         */
        int                     j_errno;

        /* The superblock buffer */
        struct buffer_head      *j_sb_buffer;
        journal_superblock_t    *j_superblock;

        /* Version of the superblock format */
        int                     j_format_version;

        /*
         * Protect the various scalars in the journal
         */
        rwlock_t                j_state_lock;

        /*
         * Number of processes waiting to create a barrier lock [j_state_lock]
         */
        int                     j_barrier_count;

        /* The barrier lock itself */
        struct mutex            j_barrier;

        /*
         * Transactions: The current running transaction...
         * [j_state_lock] [caller holding open handle]
         */
        transaction_t           *j_running_transaction;

        /*
         * the transaction we are pushing to disk
         * [j_state_lock] [caller holding open handle]
         */
        transaction_t           *j_committing_transaction;

        /*
         * ... and a linked circular list of all transactions waiting for
         * checkpointing. [j_list_lock]
         */
        transaction_t           *j_checkpoint_transactions;

        /*
         * Wait queue for waiting for a locked transaction to start committing,
         * or for a barrier lock to be released
         */
        wait_queue_head_t       j_wait_transaction_locked;

        /* Wait queue for waiting for commit to complete */
        wait_queue_head_t       j_wait_done_commit;

        /* Wait queue to trigger commit */
        wait_queue_head_t       j_wait_commit;

        /* Wait queue to wait for updates to complete */
        wait_queue_head_t       j_wait_updates;

        /* Wait queue to wait for reserved buffer credits to drop */
        wait_queue_head_t       j_wait_reserved;

        /* Semaphore for locking against concurrent checkpoints */
        struct mutex            j_checkpoint_mutex;

        /*
         * List of buffer heads used by the checkpoint routine.  This
         * was moved from jbd2_log_do_checkpoint() to reduce stack
         * usage.  Access to this array is controlled by the
         * j_checkpoint_mutex.  [j_checkpoint_mutex]
         */
        struct buffer_head      *j_chkpt_bhs[JBD2_NR_BATCH];
        
        /*
         * Journal head: identifies the first unused block in the journal.
         * [j_state_lock]
         */
        unsigned long           j_head;

        /*
         * Journal tail: identifies the oldest still-used block in the journal.
         * [j_state_lock]
         */
        unsigned long           j_tail;

        /*
         * Journal free: how many free blocks are there in the journal?
         * [j_state_lock]
         */
        unsigned long           j_free;

        /*
         * Journal start and end: the block numbers of the first usable block
         * and one beyond the last usable block in the journal. [j_state_lock]
         */
        unsigned long           j_first;
        unsigned long           j_last;

        /*
         * Device, blocksize and starting block offset for the location where we
         * store the journal.
         */
        struct block_device     *j_dev;
        int                     j_blocksize;
        unsigned long long      j_blk_offset;
        char                    j_devname[BDEVNAME_SIZE+24];

        /*
         * Device which holds the client fs.  For internal journal this will be
         * equal to j_dev.
         */
        struct block_device     *j_fs_dev;

        /* Total maximum capacity of the journal region on disk. */
        unsigned int            j_maxlen;

        /* Number of buffers reserved from the running transaction */
        atomic_t                j_reserved_credits;

        /*
         * Protects the buffer lists and internal buffer state.
         */
        spinlock_t              j_list_lock;

        /* Optional inode where we store the journal.  If present, all */
        /* journal block numbers are mapped into this inode via */
        /* bmap(). */
        struct inode            *j_inode;

        /*
         * Sequence number of the oldest transaction in the log [j_state_lock]
         */
        tid_t                   j_tail_sequence;

        /*
         * Sequence number of the next transaction to grant [j_state_lock]
         */
        tid_t                   j_transaction_sequence;

        /*
         * Sequence number of the most recently committed transaction
         * [j_state_lock].
         */
        tid_t                   j_commit_sequence;

        /*
         * Sequence number of the most recent transaction wanting commit
         * [j_state_lock]
         */
        tid_t                   j_commit_request;

        /*
         * Journal uuid: identifies the object (filesystem, LVM volume etc)
         * backed by this journal.  This will eventually be replaced by an array
         * of uuids, allowing us to index multiple devices within a single
         * journal and to perform atomic updates across them.
         */
        __u8                    j_uuid[16];

        /* Pointer to the current commit thread for this journal */
        struct task_struct      *j_task;

        /*
         * Maximum number of metadata buffers to allow in a single compound
         * commit transaction
         */
        int                     j_max_transaction_buffers;

        /*
         * What is the maximum transaction lifetime before we begin a commit?
         */
        unsigned long           j_commit_interval;

        /* The timer used to wakeup the commit thread: */
        struct timer_list       j_commit_timer;

        /*
         * The revoke table: maintains the list of revoked blocks in the
         * current transaction.  [j_revoke_lock]
         */
        spinlock_t              j_revoke_lock;
        struct jbd2_revoke_table_s *j_revoke;
        struct jbd2_revoke_table_s *j_revoke_table[2];

        /*
         * array of bhs for jbd2_journal_commit_transaction
         */
        struct buffer_head      **j_wbuf;
        int                     j_wbufsize;

        /*
         * this is the pid of hte last person to run a synchronous operation
         * through the journal
         */
        pid_t                   j_last_sync_writer;

        /*
         * the average amount of time in nanoseconds it takes to commit a
         * transaction to disk. [j_state_lock]
         */
        u64                     j_average_commit_time;

        /*
         * minimum and maximum times that we should wait for
         * additional filesystem operations to get batched into a
         * synchronous handle in microseconds
         */
        u32                     j_min_batch_time;
        u32                     j_max_batch_time;

        /* This function is called when a transaction is closed */
        void                    (*j_commit_callback)(journal_t *,
                                                     transaction_t *);

        /*
         * Journal statistics
         */
        spinlock_t              j_history_lock;
        struct proc_dir_entry   *j_proc_entry;
        struct transaction_stats_s j_stats;

        /* Failed journal commit ID */
        unsigned int            j_failed_commit;

        /*
         * An opaque pointer to fs-private information.  ext3 puts its
         * superblock pointer here
         */
        void *j_private;

        /* Reference to checksum algorithm driver via cryptoapi */
        struct crypto_shash *j_chksum_driver;

        /* Precomputed journal UUID checksum for seeding other checksums */
        __u32 j_csum_seed;
};

/* journal feature predicate functions */
#define JBD2_FEATURE_COMPAT_FUNCS(name, flagname) \
static inline bool jbd2_has_feature_##name(journal_t *j) \
{ \
        return ((j)->j_format_version >= 2 && \
                ((j)->j_superblock->s_feature_compat & \
                 cpu_to_be32(JBD2_FEATURE_COMPAT_##flagname)) != 0); \
} \
static inline void jbd2_set_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_compat |= \
                cpu_to_be32(JBD2_FEATURE_COMPAT_##flagname); \
} \
static inline void jbd2_clear_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_compat &= \
                ~cpu_to_be32(JBD2_FEATURE_COMPAT_##flagname); \
}

#define JBD2_FEATURE_RO_COMPAT_FUNCS(name, flagname) \
static inline bool jbd2_has_feature_##name(journal_t *j) \
{ \
        return ((j)->j_format_version >= 2 && \
                ((j)->j_superblock->s_feature_ro_compat & \
                 cpu_to_be32(JBD2_FEATURE_RO_COMPAT_##flagname)) != 0); \
} \
static inline void jbd2_set_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_ro_compat |= \
                cpu_to_be32(JBD2_FEATURE_RO_COMPAT_##flagname); \
} \
static inline void jbd2_clear_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_ro_compat &= \
                ~cpu_to_be32(JBD2_FEATURE_RO_COMPAT_##flagname); \
}

#define JBD2_FEATURE_INCOMPAT_FUNCS(name, flagname) \
static inline bool jbd2_has_feature_##name(journal_t *j) \
{ \
        return ((j)->j_format_version >= 2 && \
                ((j)->j_superblock->s_feature_incompat & \
                 cpu_to_be32(JBD2_FEATURE_INCOMPAT_##flagname)) != 0); \
} \
static inline void jbd2_set_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_incompat |= \
                cpu_to_be32(JBD2_FEATURE_INCOMPAT_##flagname); \
} \
static inline void jbd2_clear_feature_##name(journal_t *j) \
{ \
        (j)->j_superblock->s_feature_incompat &= \
                ~cpu_to_be32(JBD2_FEATURE_INCOMPAT_##flagname); \
}

JBD2_FEATURE_COMPAT_FUNCS(checksum,             CHECKSUM)

JBD2_FEATURE_INCOMPAT_FUNCS(revoke,             REVOKE)
JBD2_FEATURE_INCOMPAT_FUNCS(64bit,              64BIT)
JBD2_FEATURE_INCOMPAT_FUNCS(async_commit,       ASYNC_COMMIT)
JBD2_FEATURE_INCOMPAT_FUNCS(csum2,              CSUM_V2)
JBD2_FEATURE_INCOMPAT_FUNCS(csum3,              CSUM_V3)

/*
 * Journal flag definitions
 */
#define JBD2_UNMOUNT    0x001   /* Journal thread is being destroyed */
#define JBD2_ABORT      0x002   /* Journaling has been aborted for errors. */
#define JBD2_ACK_ERR    0x004   /* The errno in the sb has been acked */
#define JBD2_FLUSHED    0x008   /* The journal superblock has been flushed */
#define JBD2_LOADED     0x010   /* The journal superblock has been loaded */
#define JBD2_BARRIER    0x020   /* Use IDE barriers */
#define JBD2_ABORT_ON_SYNCDATA_ERR      0x040   /* Abort the journal on file
                                                 * data write error in ordered
                                                 * mode */
#define JBD2_REC_ERR    0x080   /* The errno in the sb has been recorded */

/*
 * Function declarations for the journaling transaction and buffer
 * management
 */

/* Filing buffers */
extern void jbd2_journal_unfile_buffer(journal_t *, struct journal_head *);
extern void __jbd2_journal_refile_buffer(struct journal_head *);
extern void jbd2_journal_refile_buffer(journal_t *, struct journal_head *);
extern void __jbd2_journal_file_buffer(struct journal_head *, transaction_t *, int);
extern void __journal_free_buffer(struct journal_head *bh);
extern void jbd2_journal_file_buffer(struct journal_head *, transaction_t *, int);
extern void __journal_clean_data_list(transaction_t *transaction);
static inline void jbd2_file_log_bh(struct list_head *head, struct buffer_head *bh)
{
        list_add_tail(&bh->b_assoc_buffers, head);
}
static inline void jbd2_unfile_log_bh(struct buffer_head *bh)
{
        list_del_init(&bh->b_assoc_buffers);
}

/* Log buffer allocation */
struct buffer_head *jbd2_journal_get_descriptor_buffer(transaction_t *, int);
void jbd2_descriptor_block_csum_set(journal_t *, struct buffer_head *);
int jbd2_journal_next_log_block(journal_t *, unsigned long long *);
int jbd2_journal_get_log_tail(journal_t *journal, tid_t *tid,
                              unsigned long *block);
int __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);
void jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);

/* Commit management */
extern void jbd2_journal_commit_transaction(journal_t *);

/* Checkpoint list management */
void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy);
int __jbd2_journal_remove_checkpoint(struct journal_head *);
void jbd2_journal_destroy_checkpoint(journal_t *journal);
void __jbd2_journal_insert_checkpoint(struct journal_head *, transaction_t *);


/*
 * Triggers
 */

struct jbd2_buffer_trigger_type {
        /*
         * Fired a the moment data to write to the journal are known to be
         * stable - so either at the moment b_frozen_data is created or just
         * before a buffer is written to the journal.  mapped_data is a mapped
         * buffer that is the frozen data for commit.
         */
        void (*t_frozen)(struct jbd2_buffer_trigger_type *type,
                         struct buffer_head *bh, void *mapped_data,
                         size_t size);

        /*
         * Fired during journal abort for dirty buffers that will not be
         * committed.
         */
        void (*t_abort)(struct jbd2_buffer_trigger_type *type,
                        struct buffer_head *bh);
};

extern void jbd2_buffer_frozen_trigger(struct journal_head *jh,
                                       void *mapped_data,
                                       struct jbd2_buffer_trigger_type *triggers);
extern void jbd2_buffer_abort_trigger(struct journal_head *jh,
                                      struct jbd2_buffer_trigger_type *triggers);

/* Buffer IO */
extern int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
                                              struct journal_head *jh_in,
                                              struct buffer_head **bh_out,
                                              sector_t blocknr);

/* Transaction locking */
extern void             __wait_on_journal (journal_t *);

/* Transaction cache support */
extern void jbd2_journal_destroy_transaction_cache(void);
extern int  jbd2_journal_init_transaction_cache(void);
extern void jbd2_journal_free_transaction(transaction_t *);

/*
 * Journal locking.
 *
 * We need to lock the journal during transaction state changes so that nobody
 * ever tries to take a handle on the running transaction while we are in the
 * middle of moving it to the commit phase.  j_state_lock does this.
 *
 * Note that the locking is completely interrupt unsafe.  We never touch
 * journal structures from interrupts.
 */

static inline handle_t *journal_current_handle(void)
{
        return current->journal_info;
}

/* The journaling code user interface:
 *
 * Create and destroy handles
 * Register buffer modifications against the current transaction.
 */

extern handle_t *jbd2_journal_start(journal_t *, int nblocks);
extern handle_t *jbd2__journal_start(journal_t *, int blocks, int rsv_blocks,
                                     gfp_t gfp_mask, unsigned int type,
                                     unsigned int line_no);
extern int       jbd2_journal_restart(handle_t *, int nblocks);
extern int       jbd2__journal_restart(handle_t *, int nblocks, gfp_t gfp_mask);
extern int       jbd2_journal_start_reserved(handle_t *handle,
                                unsigned int type, unsigned int line_no);
extern void      jbd2_journal_free_reserved(handle_t *handle);
extern int       jbd2_journal_extend (handle_t *, int nblocks);
extern int       jbd2_journal_get_write_access(handle_t *, struct buffer_head *);
extern int       jbd2_journal_get_create_access (handle_t *, struct buffer_head *);
extern int       jbd2_journal_get_undo_access(handle_t *, struct buffer_head *);
void             jbd2_journal_set_triggers(struct buffer_head *,
                                           struct jbd2_buffer_trigger_type *type);
extern int       jbd2_journal_dirty_metadata (handle_t *, struct buffer_head *);
extern int       jbd2_journal_forget (handle_t *, struct buffer_head *);
extern void      journal_sync_buffer (struct buffer_head *);
extern int       jbd2_journal_invalidatepage(journal_t *,
                                struct page *, unsigned int, unsigned int);
extern int       jbd2_journal_try_to_free_buffers(journal_t *, struct page *, gfp_t);
extern int       jbd2_journal_stop(handle_t *);
extern int       jbd2_journal_flush (journal_t *);
extern void      jbd2_journal_lock_updates (journal_t *);
extern void      jbd2_journal_unlock_updates (journal_t *);

extern journal_t * jbd2_journal_init_dev(struct block_device *bdev,
                                struct block_device *fs_dev,
                                unsigned long long start, int len, int bsize);
extern journal_t * jbd2_journal_init_inode (struct inode *);
extern int         jbd2_journal_update_format (journal_t *);
extern int         jbd2_journal_check_used_features
                   (journal_t *, unsigned long, unsigned long, unsigned long);
extern int         jbd2_journal_check_available_features
                   (journal_t *, unsigned long, unsigned long, unsigned long);
extern int         jbd2_journal_set_features
                   (journal_t *, unsigned long, unsigned long, unsigned long);
extern void        jbd2_journal_clear_features
                   (journal_t *, unsigned long, unsigned long, unsigned long);
extern int         jbd2_journal_load       (journal_t *journal);
extern int         jbd2_journal_destroy    (journal_t *);
extern int         jbd2_journal_recover    (journal_t *journal);
extern int         jbd2_journal_wipe       (journal_t *, int);
extern int         jbd2_journal_skip_recovery   (journal_t *);
extern void        jbd2_journal_update_sb_errno(journal_t *);
extern int         jbd2_journal_update_sb_log_tail      (journal_t *, tid_t,
                                unsigned long, int);
extern void        __jbd2_journal_abort_hard    (journal_t *);
extern void        jbd2_journal_abort      (journal_t *, int);
extern int         jbd2_journal_errno      (journal_t *);
extern void        jbd2_journal_ack_err    (journal_t *);
extern int         jbd2_journal_clear_err  (journal_t *);
extern int         jbd2_journal_bmap(journal_t *, unsigned long, unsigned long long *);
extern int         jbd2_journal_force_commit(journal_t *);
extern int         jbd2_journal_force_commit_nested(journal_t *);
extern int         jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *inode);
extern int         jbd2_journal_begin_ordered_truncate(journal_t *journal,
                                struct jbd2_inode *inode, loff_t new_size);
extern void        jbd2_journal_init_jbd_inode(struct jbd2_inode *jinode, struct inode *inode);
extern void        jbd2_journal_release_jbd_inode(journal_t *journal, struct jbd2_inode *jinode);

/*
 * journal_head management
 */
struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh);
struct journal_head *jbd2_journal_grab_journal_head(struct buffer_head *bh);
void jbd2_journal_put_journal_head(struct journal_head *jh);

/*
 * handle management
 */
extern struct kmem_cache *jbd2_handle_cache;

static inline handle_t *jbd2_alloc_handle(gfp_t gfp_flags)
{
        return kmem_cache_zalloc(jbd2_handle_cache, gfp_flags);
}

static inline void jbd2_free_handle(handle_t *handle)
{
        kmem_cache_free(jbd2_handle_cache, handle);
}

/*
 * jbd2_inode management (optional, for those file systems that want to use
 * dynamically allocated jbd2_inode structures)
 */
extern struct kmem_cache *jbd2_inode_cache;

static inline struct jbd2_inode *jbd2_alloc_inode(gfp_t gfp_flags)
{
        return kmem_cache_alloc(jbd2_inode_cache, gfp_flags);
}

static inline void jbd2_free_inode(struct jbd2_inode *jinode)
{
        kmem_cache_free(jbd2_inode_cache, jinode);
}

/* Primary revoke support */
#define JOURNAL_REVOKE_DEFAULT_HASH 256
extern int         jbd2_journal_init_revoke(journal_t *, int);
extern void        jbd2_journal_destroy_revoke_caches(void);
extern int         jbd2_journal_init_revoke_caches(void);

extern void        jbd2_journal_destroy_revoke(journal_t *);
extern int         jbd2_journal_revoke (handle_t *, unsigned long long, struct buffer_head *);
extern int         jbd2_journal_cancel_revoke(handle_t *, struct journal_head *);
extern void        jbd2_journal_write_revoke_records(transaction_t *transaction,
                                                     struct list_head *log_bufs);

/* Recovery revoke support */
extern int      jbd2_journal_set_revoke(journal_t *, unsigned long long, tid_t);
extern int      jbd2_journal_test_revoke(journal_t *, unsigned long long, tid_t);
extern void     jbd2_journal_clear_revoke(journal_t *);
extern void     jbd2_journal_switch_revoke_table(journal_t *journal);
extern void     jbd2_clear_buffer_revoked_flags(journal_t *journal);

/*
 * The log thread user interface:
 *
 * Request space in the current transaction, and force transaction commit
 * transitions on demand.
 */

int jbd2_log_start_commit(journal_t *journal, tid_t tid);
int __jbd2_log_start_commit(journal_t *journal, tid_t tid);
int jbd2_journal_start_commit(journal_t *journal, tid_t *tid);
int jbd2_log_wait_commit(journal_t *journal, tid_t tid);
int jbd2_complete_transaction(journal_t *journal, tid_t tid);
int jbd2_log_do_checkpoint(journal_t *journal);
int jbd2_trans_will_send_data_barrier(journal_t *journal, tid_t tid);

void __jbd2_log_wait_for_space(journal_t *journal);
extern void __jbd2_journal_drop_transaction(journal_t *, transaction_t *);
extern int jbd2_cleanup_journal_tail(journal_t *);

/*
 * is_journal_abort
 *
 * Simple test wrapper function to test the JBD2_ABORT state flag.  This
 * bit, when set, indicates that we have had a fatal error somewhere,
 * either inside the journaling layer or indicated to us by the client
 * (eg. ext3), and that we and should not commit any further
 * transactions.
 */

static inline int is_journal_aborted(journal_t *journal)
{
        return journal->j_flags & JBD2_ABORT;
}

static inline int is_handle_aborted(handle_t *handle)
{
        if (handle->h_aborted || !handle->h_transaction)
                return 1;
        return is_journal_aborted(handle->h_transaction->t_journal);
}

static inline void jbd2_journal_abort_handle(handle_t *handle)
{
        handle->h_aborted = 1;
}

#endif /* __KERNEL__   */

/* Comparison functions for transaction IDs: perform comparisons using
 * modulo arithmetic so that they work over sequence number wraps. */

static inline int tid_gt(tid_t x, tid_t y)
{
        int difference = (x - y);
        return (difference > 0);
}

static inline int tid_geq(tid_t x, tid_t y)
{
        int difference = (x - y);
        return (difference >= 0);
}

extern int jbd2_journal_blocks_per_page(struct inode *inode);
extern size_t journal_tag_bytes(journal_t *journal);

static inline bool jbd2_journal_has_csum_v2or3_feature(journal_t *j)
{
        return jbd2_has_feature_csum2(j) || jbd2_has_feature_csum3(j);
}

static inline int jbd2_journal_has_csum_v2or3(journal_t *journal)
{
        WARN_ON_ONCE(jbd2_journal_has_csum_v2or3_feature(journal) &&
                     journal->j_chksum_driver == NULL);

        return journal->j_chksum_driver != NULL;
}

/*
 * We reserve t_outstanding_credits >> JBD2_CONTROL_BLOCKS_SHIFT for
 * transaction control blocks.
 */
#define JBD2_CONTROL_BLOCKS_SHIFT 5

/*
 * Return the minimum number of blocks which must be free in the journal
 * before a new transaction may be started.  Must be called under j_state_lock.
 */
static inline int jbd2_space_needed(journal_t *journal)
{
        int nblocks = journal->j_max_transaction_buffers;
        return nblocks + (nblocks >> JBD2_CONTROL_BLOCKS_SHIFT);
}

/*
 * Return number of free blocks in the log. Must be called under j_state_lock.
 */
static inline unsigned long jbd2_log_space_left(journal_t *journal)
{
        /* Allow for rounding errors */
        unsigned long free = journal->j_free - 32;

        if (journal->j_committing_transaction) {
                unsigned long committing = atomic_read(&journal->
                        j_committing_transaction->t_outstanding_credits);

                /* Transaction + control blocks */
                free -= committing + (committing >> JBD2_CONTROL_BLOCKS_SHIFT);
        }
        return free;
}

/*
 * Definitions which augment the buffer_head layer
 */

/* journaling buffer types */
#define BJ_None         0       /* Not journaled */
#define BJ_Metadata     1       /* Normal journaled metadata */
#define BJ_Forget       2       /* Buffer superseded by this transaction */
#define BJ_Shadow       3       /* Buffer contents being shadowed to the log */
#define BJ_Reserved     4       /* Buffer is reserved for access by journal */
#define BJ_Types        5

extern int jbd_blocks_per_page(struct inode *inode);

/* JBD uses a CRC32 checksum */
#define JBD_MAX_CHECKSUM_SIZE 4

static inline u32 jbd2_chksum(journal_t *journal, u32 crc,
                              const void *address, unsigned int length)
{
        struct {
                struct shash_desc shash;
                char ctx[JBD_MAX_CHECKSUM_SIZE];
        } desc;
        int err;

        BUG_ON(crypto_shash_descsize(journal->j_chksum_driver) >
                JBD_MAX_CHECKSUM_SIZE);

        desc.shash.tfm = journal->j_chksum_driver;
        desc.shash.flags = 0;
        *(u32 *)desc.ctx = crc;

        err = crypto_shash_update(&desc.shash, address, length);
        BUG_ON(err);

        return *(u32 *)desc.ctx;
}

/* Return most recent uncommitted transaction */
static inline tid_t  jbd2_get_latest_transaction(journal_t *journal)
{
        tid_t tid;

        read_lock(&journal->j_state_lock);
        tid = journal->j_commit_request;
        if (journal->j_running_transaction)
                tid = journal->j_running_transaction->t_tid;
        read_unlock(&journal->j_state_lock);
        return tid;
}

#ifdef __KERNEL__

#define buffer_trace_init(bh)   do {} while (0)
#define print_buffer_fields(bh) do {} while (0)
#define print_buffer_trace(bh)  do {} while (0)
#define BUFFER_TRACE(bh, info)  do {} while (0)
#define BUFFER_TRACE2(bh, bh2, info)    do {} while (0)
#define JBUFFER_TRACE(jh, info) do {} while (0)

#endif  /* __KERNEL__ */

#define EFSBADCRC       EBADMSG         /* Bad CRC detected */
#define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */

#endif  /* _LINUX_JBD2_H */