projects / deliverable / linux.git / blame
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|---|---|---|
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1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | ||
| 3 | .. _frontend_f_open: | |
| 4 | ||
| 5 | ******************* | |
| 6 | DVB frontend open() | |
| 7 | ******************* | |
| 8 | ||
| 15e7d615 | 9 | Name |
| 586027ce | 10 | ==== |
| 5377d91f | 11 | |
| 586027ce | 12 | fe-open - Open a frontend device |
| 5377d91f | 13 | |
| 15e7d615 MCC |
14 | |
| 15 | Synopsis | |
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16 | ======== |
| 17 | ||
| 18 | .. code-block:: c | |
| 19 | ||
| 20 | #include <fcntl.h> | |
| 21 | ||
| 22 | ||
| b7e67f6c | 23 | .. cpp:function:: int open( const char *device_name, int flags ) |
| 5377d91f | 24 | |
| 586027ce | 25 | |
| 15e7d615 | 26 | Arguments |
| 5377d91f MH |
27 | ========= |
| 28 | ||
| 29 | ``device_name`` | |
| 30 | Device to be opened. | |
| 31 | ||
| 32 | ``flags`` | |
| 33 | Open flags. Access can either be ``O_RDWR`` or ``O_RDONLY``. | |
| 34 | ||
| 35 | Multiple opens are allowed with ``O_RDONLY``. In this mode, only | |
| 36 | query and read ioctls are allowed. | |
| 37 | ||
| 38 | Only one open is allowed in ``O_RDWR``. In this mode, all ioctls are | |
| 39 | allowed. | |
| 40 | ||
| 41 | When the ``O_NONBLOCK`` flag is given, the system calls may return | |
| cdb4af0f | 42 | ``EAGAIN`` error code when no data is available or when the device |
| 5377d91f MH |
43 | driver is temporarily busy. |
| 44 | ||
| 45 | Other flags have no effect. | |
| 46 | ||
| 47 | ||
| 15e7d615 | 48 | Description |
| 5377d91f MH |
49 | =========== |
| 50 | ||
| 51 | This system call opens a named frontend device | |
| 52 | (``/dev/dvb/adapter?/frontend?``) for subsequent use. Usually the first | |
| 53 | thing to do after a successful open is to find out the frontend type | |
| 7347081e | 54 | with :ref:`FE_GET_INFO`. |
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55 | |
| 56 | The device can be opened in read-only mode, which only allows monitoring | |
| 57 | of device status and statistics, or read/write mode, which allows any | |
| 58 | kind of use (e.g. performing tuning operations.) | |
| 59 | ||
| 60 | In a system with multiple front-ends, it is usually the case that | |
| 61 | multiple devices cannot be open in read/write mode simultaneously. As | |
| 62 | long as a front-end device is opened in read/write mode, other open() | |
| 63 | calls in read/write mode will either fail or block, depending on whether | |
| 64 | non-blocking or blocking mode was specified. A front-end device opened | |
| 65 | in blocking mode can later be put into non-blocking mode (and vice | |
| 66 | versa) using the F_SETFL command of the fcntl system call. This is a | |
| 67 | standard system call, documented in the Linux manual page for fcntl. | |
| 68 | When an open() call has succeeded, the device will be ready for use in | |
| 69 | the specified mode. This implies that the corresponding hardware is | |
| 70 | powered up, and that other front-ends may have been powered down to make | |
| 71 | that possible. | |
| 72 | ||
| 73 | ||
| 15e7d615 | 74 | Return Value |
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75 | ============ |
| 76 | ||
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77 | On success :ref:`open() <frontend_f_open>` returns the new file descriptor. |
| 78 | On error, -1 is returned, and the ``errno`` variable is set appropriately. | |
| 79 | ||
| 5377d91f MH |
80 | Possible error codes are: |
| 81 | ||
| 82 | EACCES | |
| 83 | The caller has no permission to access the device. | |
| 84 | ||
| 85 | EBUSY | |
| 86 | The the device driver is already in use. | |
| 87 | ||
| 88 | ENXIO | |
| 89 | No device corresponding to this device special file exists. | |
| 90 | ||
| 91 | ENOMEM | |
| 92 | Not enough kernel memory was available to complete the request. | |
| 93 | ||
| 94 | EMFILE | |
| 95 | The process already has the maximum number of files open. | |
| 96 | ||
| 97 | ENFILE | |
| 98 | The limit on the total number of files open on the system has been | |
| 99 | reached. | |
| 100 | ||
| 101 | ENODEV | |
| 102 | The device got removed. |