doc: update documentation for swap_activate and swap_rw

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swap_activate() has been out-of-date for a long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>

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index c26d854275a0ec399c610af4d356d0a9d9ef0e21..ef2efa1cb4ec532da9413ccf32cd841c7922afc9 100644 (file)
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -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
 ====================
 

diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 794bd1a66bfbdfed8e4b95c003ac7a6a90de1b9e..d4bd213d215b4b00f808347e0ca90cc9f5ae8362 100644 (file)
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -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
 ===============