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doc: update documentation for swap_activate and swap_rw

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This documentation for ->swap_activate() has been out-of-date for a long
time.  This patch updates it to match recent changes, and adds
documentation for the associated ->swap_rw()

Link: https://lkml.kernel.org/r/164859778126.29473.6778751233552859461.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
NeilBrown 2022-05-09 18:20:48 -07:00 committed by akpm
parent 7eadabc05d
commit cba738f649
2 changed files with 24 additions and 11 deletions
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18
Documentation/filesystems/locking.rst
View File

@ -258,8 +258,9 @@ prototypes::
int (*launder_folio)(struct folio *);
bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count);
int (*error_remove_page)(struct address_space *, struct page *);
int (*swap_activate)(struct file *);
int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
int (*swap_deactivate)(struct file *);
int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
locking rules:
All except dirty_folio and freepage may block
@ -287,6 +288,7 @@ is_partially_uptodate: yes
error_remove_page: yes
swap_activate: no
swap_deactivate: no
swap_rw: yes, unlocks
====================== ======================== ========= ===============
->write_begin(), ->write_end() and ->readpage() may be called from
@ -386,15 +388,19 @@ cleaned, or an error value if not. Note that in order to prevent the folio
getting mapped back in and redirtied, it needs to be kept locked
across the entire operation.
->swap_activate will be called with a non-zero argument on
files backing (non block device backed) swapfiles. A return value
of zero indicates success, in which case this file can be used for
backing swapspace. The swapspace operations will be proxied to the
address space operations.
->swap_activate() will be called to prepare the given file for swap. It
should perform any validation and preparation necessary to ensure that
writes can be performed with minimal memory allocation. It should call
add_swap_extent(), or the helper iomap_swapfile_activate(), and return
the number of extents added. If IO should be submitted through
->swap_rw(), it should set SWP_FS_OPS, otherwise IO will be submitted
directly to the block device ``sis->bdev``.
->swap_deactivate() will be called in the sys_swapoff()
path after ->swap_activate() returned success.
->swap_rw will be called for swap IO if SWP_FS_OPS was set by ->swap_activate().
file_lock_operations
====================

17
Documentation/filesystems/vfs.rst
View File

@ -749,8 +749,9 @@ cache in your filesystem. The following members are defined:
size_t count);
void (*is_dirty_writeback) (struct page *, bool *, bool *);
int (*error_remove_page) (struct mapping *mapping, struct page *page);
int (*swap_activate)(struct file *);
int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
int (*swap_deactivate)(struct file *);
int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
};
``writepage``
@ -952,15 +953,21 @@ cache in your filesystem. The following members are defined:
unless you have them locked or reference counts increased.
``swap_activate``
Called when swapon is used on a file to allocate space if
necessary and pin the block lookup information in memory. A
return value of zero indicates success, in which case this file
can be used to back swapspace.
Called to prepare the given file for swap. It should perform
any validation and preparation necessary to ensure that writes
can be performed with minimal memory allocation. It should call
add_swap_extent(), or the helper iomap_swapfile_activate(), and
return the number of extents added. If IO should be submitted
through ->swap_rw(), it should set SWP_FS_OPS, otherwise IO will
be submitted directly to the block device ``sis->bdev``.
``swap_deactivate``
Called during swapoff on files where swap_activate was
successful.
``swap_rw``
Called to read or write swap pages when SWP_FS_OPS is set.
The File Object
===============