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Diffstat (limited to 'Documentation/filesystems/netfs_library.rst')
| -rw-r--r-- | Documentation/filesystems/netfs_library.rst | 32 |
1 files changed, 26 insertions, 6 deletions
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst index 375baca7edcd..4f373a8ec47b 100644 --- a/Documentation/filesystems/netfs_library.rst +++ b/Documentation/filesystems/netfs_library.rst @@ -454,13 +454,18 @@ operation table looks like the following:: void *term_func_priv); int (*prepare_write)(struct netfs_cache_resources *cres, - loff_t *_start, size_t *_len, loff_t i_size); + loff_t *_start, size_t *_len, loff_t i_size, + bool no_space_allocated_yet); int (*write)(struct netfs_cache_resources *cres, loff_t start_pos, struct iov_iter *iter, netfs_io_terminated_t term_func, void *term_func_priv); + + int (*query_occupancy)(struct netfs_cache_resources *cres, + loff_t start, size_t len, size_t granularity, + loff_t *_data_start, size_t *_data_len); }; With a termination handler function pointer:: @@ -515,11 +520,14 @@ The methods defined in the table are: * ``prepare_write()`` - [Required] Called to adjust a write to the cache and check that there is - sufficient space in the cache. The start and length values indicate the - size of the write that netfslib is proposing, and this can be adjusted by - the cache to respect DIO boundaries. The file size is passed for - information. + [Required] Called to prepare a write to the cache to take place. This + involves checking to see whether the cache has sufficient space to honour + the write. ``*_start`` and ``*_len`` indicate the region to be written; the + region can be shrunk or it can be expanded to a page boundary either way as + necessary to align for direct I/O. i_size holds the size of the object and + is provided for reference. no_space_allocated_yet is set to true if the + caller is certain that no data has been written to that region - for example + if it tried to do a read from there already. * ``write()`` @@ -532,6 +540,18 @@ The methods defined in the table are: indicating whether the termination is definitely happening in the caller's context. + * ``query_occupancy()`` + + [Required] Called to find out where the next piece of data is within a + particular region of the cache. The start and length of the region to be + queried are passed in, along with the granularity to which the answer needs + to be aligned. The function passes back the start and length of the data, + if any, available within that region. Note that there may be a hole at the + front. + + It returns 0 if some data was found, -ENODATA if there was no usable data + within the region or -ENOBUFS if there is no caching on this file. + Note that these methods are passed a pointer to the cache resource structure, not the read request structure as they could be used in other situations where there isn't a read request structure as well, such as writing dirty data to the |