On 25.05.2018 00:41, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
>
> The documentation for these functions is wrong in several ways:
>
> - swap_activate() is called with the inode locked
> - swap_activate() takes a swap_info_struct * and a sector_t *
> - swap_activate() can also return a positive number of extents it added
> itself
> - swap_deactivate() does not return anything
>
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
> ---
> Documentation/filesystems/Locking | 17 +++++++----------
> Documentation/filesystems/vfs.txt | 12 ++++++++----
> 2 files changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
> index 75d2d57e2c44..7f009e98fa3c 100644
> --- a/Documentation/filesystems/Locking
> +++ b/Documentation/filesystems/Locking
> @@ -211,8 +211,9 @@ prototypes:
> int (*launder_page)(struct page *);
> int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
> int (*error_remove_page)(struct address_space *, struct page *);
> - int (*swap_activate)(struct file *);
> - int (*swap_deactivate)(struct file *);
> + int (*swap_activate)(struct swap_info_struct *, struct file *,
> + sector_t *);
> + void (*swap_deactivate)(struct file *);
>
> locking rules:
> All except set_page_dirty and freepage may block
> @@ -236,8 +237,8 @@ putback_page: yes
> launder_page: yes
> is_partially_uptodate: yes
> error_remove_page: yes
> -swap_activate: no
> -swap_deactivate: no
> +swap_activate: yes
> +swap_deactivate: no
>
> ->write_begin(), ->write_end() and ->readpage() may be called from
> the request handler (/dev/loop).
> @@ -334,14 +335,10 @@ cleaned, or an error value if not. Note that in order to prevent the page
> 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 is called from sys_swapon() with the inode locked.
>
> ->swap_deactivate() will be called in the sys_swapoff()
> -path after ->swap_activate() returned success.
> +path after ->swap_activate() returned success. The inode is not locked.
>
> ----------------------- file_lock_operations ------------------------------
> prototypes:
> diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
> index 5fd325df59e2..0149109d94d1 100644
> --- a/Documentation/filesystems/vfs.txt
> +++ b/Documentation/filesystems/vfs.txt
> @@ -650,8 +650,9 @@ struct address_space_operations {
> unsigned long);
> 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_deactivate)(struct file *);
> + int (*swap_activate)(struct swap_info_struct *, struct file *,
> + sector_t *);
> + void (*swap_deactivate)(struct file *);
> };
>
> writepage: called by the VM to write a dirty page to backing store.
> @@ -828,8 +829,11 @@ struct address_space_operations {
>
> 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.
> + memory. If this returns zero, the swap system will call the address
> + space operations ->readpage() and ->direct_IO(). Alternatively, this
> + may call add_swap_extent() and return the number of extents added, in
> + which case the swap system will use the provided blocks directly
> + instead of going through the filesystem.
>
> swap_deactivate: Called during swapoff on files where swap_activate
> was successful.
>
