include/babeltrace/mmap-align.h

   1 #ifndef _BABELTRACE_MMAP_ALIGN_H
   2 #define _BABELTRACE_MMAP_ALIGN_H
   3
   4 /*
   5  * BabelTrace mmap-align.h - mmap alignment header
   6  *
   7  * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a copy
  10  * of this software and associated documentation files (the "Software"), to deal
  11  * in the Software without restriction, including without limitation the rights
  12  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  13  * copies of the Software, and to permit persons to whom the Software is
  14  * furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included in
  17  * all copies or substantial portions of the Software.
  18  */
  19
  20 #include <babeltrace/align.h>
  21 #include <stdlib.h>
  22 #include <sys/mman.h>
  23
  24 /*
  25  * This header implements a wrapper over mmap (mmap_align) that memory
  26  * maps a file region that is not necessarily multiple of the page size.
  27  * It returns a structure (instead of a pointer) that contains the mmap
  28  * pointer (page-aligned) and a pointer to the offset requested within
  29  * that page. Note: in the current implementation, the "addr" parameter
  30  * cannot be forced, so we allocate at an address chosen by the OS.
  31  */
  32
  33 struct mmap_align {
  34         void *page_aligned_addr;        /* mmap address, aligned to floor */
  35         size_t page_aligned_length;     /* mmap length, containing range */
  36
  37         void *addr;                     /* virtual mmap address */
  38         size_t length;                  /* virtual mmap length */
  39 };
  40
  41 static inline
  42 struct mmap_align *mmap_align(size_t length, int prot,
  43                 int flags, int fd, off_t offset)
  44 {
  45         struct mmap_align *mma;
  46         off_t page_aligned_offset;      /* mmap offset, aligned to floor */
  47
  48         mma = malloc(sizeof(*mma));
  49         if (!mma)
  50                 return MAP_FAILED;
  51         mma->length = length;
  52         page_aligned_offset = ALIGN_FLOOR(offset, PAGE_SIZE);
  53         /*
  54          * Page aligned length needs to contain the requested range.
  55          * E.g., for a small range that fits within a single page, we might
  56          * require a 2 pages page_aligned_length if the range crosses a page
  57          * boundary.
  58          */
  59         mma->page_aligned_length = ALIGN(length + offset - page_aligned_offset, PAGE_SIZE);
  60         mma->page_aligned_addr = mmap(NULL, mma->page_aligned_length,
  61                 prot, flags, fd, page_aligned_offset);
  62         if (mma->page_aligned_addr == (void *) -1UL) {
  63                 free(mma);
  64                 return MAP_FAILED;
  65         }
  66         mma->addr = mma->page_aligned_addr + (offset - page_aligned_offset);
  67         return mma;
  68 }
  69
  70 static inline
  71 int munmap_align(struct mmap_align *mma)
  72 {
  73         void *page_aligned_addr;
  74         size_t page_aligned_length;
  75
  76         page_aligned_addr = mma->page_aligned_addr;
  77         page_aligned_length = mma->page_aligned_length;
  78         free(mma);
  79         return munmap(page_aligned_addr, page_aligned_length);
  80 }
  81
  82 static inline
  83 void *mmap_align_addr(struct mmap_align *mma)
  84 {
  85         return mma->addr;
  86 }
  87
  88 /*
  89  * Helper for special-cases, normally unused.
  90  */
  91 static inline
  92 void mmap_align_set_addr(struct mmap_align *mma, void *addr)
  93 {
  94         mma->addr = addr;
  95 }
  96
  97 #endif /* _BABELTRACE_MMAP_ALIGN_H */