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Diffstat (limited to 'Documentation/filesystems/netfs_library.rst')
| -rw-r--r-- | Documentation/filesystems/netfs_library.rst | 95 |
1 files changed, 56 insertions, 39 deletions
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst index bb68d39f03b7..375baca7edcd 100644 --- a/Documentation/filesystems/netfs_library.rst +++ b/Documentation/filesystems/netfs_library.rst @@ -1,7 +1,7 @@ .. SPDX-License-Identifier: GPL-2.0 ================================= -NETWORK FILESYSTEM HELPER LIBRARY +Network Filesystem Helper Library ================================= .. Contents: @@ -37,22 +37,22 @@ into a common call framework. The following services are provided: - * Handles transparent huge pages (THPs). + * Handle folios that span multiple pages. - * Insulates the netfs from VM interface changes. + * Insulate the netfs from VM interface changes. - * Allows the netfs to arbitrarily split reads up into pieces, even ones that - don't match page sizes or page alignments and that may cross pages. + * Allow the netfs to arbitrarily split reads up into pieces, even ones that + don't match folio sizes or folio alignments and that may cross folios. - * Allows the netfs to expand a readahead request in both directions to meet - its needs. + * Allow the netfs to expand a readahead request in both directions to meet its + needs. - * Allows the netfs to partially fulfil a read, which will then be resubmitted. + * Allow the netfs to partially fulfil a read, which will then be resubmitted. - * Handles local caching, allowing cached data and server-read data to be + * Handle local caching, allowing cached data and server-read data to be interleaved for a single request. - * Handles clearing of bufferage that aren't on the server. + * Handle clearing of bufferage that aren't on the server. * Handle retrying of reads that failed, switching reads from the cache to the server as necessary. @@ -70,22 +70,22 @@ Read Helper Functions Three read helpers are provided:: - * void netfs_readahead(struct readahead_control *ractl, - const struct netfs_read_request_ops *ops, - void *netfs_priv);`` - * int netfs_readpage(struct file *file, - struct page *page, - const struct netfs_read_request_ops *ops, - void *netfs_priv); - * int netfs_write_begin(struct file *file, - struct address_space *mapping, - loff_t pos, - unsigned int len, - unsigned int flags, - struct page **_page, - void **_fsdata, - const struct netfs_read_request_ops *ops, - void *netfs_priv); + void netfs_readahead(struct readahead_control *ractl, + const struct netfs_read_request_ops *ops, + void *netfs_priv); + int netfs_readpage(struct file *file, + struct folio *folio, + const struct netfs_read_request_ops *ops, + void *netfs_priv); + int netfs_write_begin(struct file *file, + struct address_space *mapping, + loff_t pos, + unsigned int len, + unsigned int flags, + struct folio **_folio, + void **_fsdata, + const struct netfs_read_request_ops *ops, + void *netfs_priv); Each corresponds to a VM operation, with the addition of a couple of parameters for the use of the read helpers: @@ -103,8 +103,8 @@ Both of these values will be stored into the read request structure. For ->readahead() and ->readpage(), the network filesystem should just jump into the corresponding read helper; whereas for ->write_begin(), it may be a little more complicated as the network filesystem might want to flush -conflicting writes or track dirty data and needs to put the acquired page if an -error occurs after calling the helper. +conflicting writes or track dirty data and needs to put the acquired folio if +an error occurs after calling the helper. The helpers manage the read request, calling back into the network filesystem through the suppplied table of operations. Waits will be performed as @@ -253,7 +253,7 @@ through which it can issue requests and negotiate:: void (*issue_op)(struct netfs_read_subrequest *subreq); bool (*is_still_valid)(struct netfs_read_request *rreq); int (*check_write_begin)(struct file *file, loff_t pos, unsigned len, - struct page *page, void **_fsdata); + struct folio *folio, void **_fsdata); void (*done)(struct netfs_read_request *rreq); void (*cleanup)(struct address_space *mapping, void *netfs_priv); }; @@ -313,13 +313,14 @@ The operations are as follows: There is no return value; the netfs_subreq_terminated() function should be called to indicate whether or not the operation succeeded and how much data - it transferred. The filesystem also should not deal with setting pages + it transferred. The filesystem also should not deal with setting folios uptodate, unlocking them or dropping their refs - the helpers need to deal with this as they have to coordinate with copying to the local cache. - Note that the helpers have the pages locked, but not pinned. It is possible - to use the ITER_XARRAY iov iterator to refer to the range of the inode that - is being operated upon without the need to allocate large bvec tables. + Note that the helpers have the folios locked, but not pinned. It is + possible to use the ITER_XARRAY iov iterator to refer to the range of the + inode that is being operated upon without the need to allocate large bvec + tables. * ``is_still_valid()`` @@ -330,15 +331,15 @@ The operations are as follows: * ``check_write_begin()`` [Optional] This is called from the netfs_write_begin() helper once it has - allocated/grabbed the page to be modified to allow the filesystem to flush + allocated/grabbed the folio to be modified to allow the filesystem to flush conflicting state before allowing it to be modified. - It should return 0 if everything is now fine, -EAGAIN if the page should be + It should return 0 if everything is now fine, -EAGAIN if the folio should be regrabbed and any other error code to abort the operation. * ``done`` - [Optional] This is called after the pages in the request have all been + [Optional] This is called after the folios in the request have all been unlocked (and marked uptodate if applicable). * ``cleanup`` @@ -390,7 +391,7 @@ The read helpers work by the following general procedure: * If NETFS_SREQ_CLEAR_TAIL was set, a short read will be cleared to the end of the slice instead of reissuing. - * Once the data is read, the pages that have been fully read/cleared: + * Once the data is read, the folios that have been fully read/cleared: * Will be marked uptodate. @@ -398,11 +399,11 @@ The read helpers work by the following general procedure: * Unlocked - * Any pages that need writing to the cache will then have DIO writes issued. + * Any folios that need writing to the cache will then have DIO writes issued. * Synchronous operations will wait for reading to be complete. - * Writes to the cache will proceed asynchronously and the pages will have the + * Writes to the cache will proceed asynchronously and the folios will have the PG_fscache mark removed when that completes. * The request structures will be cleaned up when everything has completed. @@ -452,6 +453,9 @@ operation table looks like the following:: netfs_io_terminated_t term_func, void *term_func_priv); + int (*prepare_write)(struct netfs_cache_resources *cres, + loff_t *_start, size_t *_len, loff_t i_size); + int (*write)(struct netfs_cache_resources *cres, loff_t start_pos, struct iov_iter *iter, @@ -509,6 +513,14 @@ The methods defined in the table are: indicating whether the termination is definitely happening in the caller's context. + * ``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. + * ``write()`` [Required] Called to write to the cache. The start file offset is given @@ -525,4 +537,9 @@ 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 cache. + +API Function Reference +====================== + .. kernel-doc:: include/linux/netfs.h +.. kernel-doc:: fs/netfs/read_helper.c |