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-rw-r--r--Documentation/filesystems/vfs.rst15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 7d4d09dd5e6d..ed17771c212b 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined:
int (*readpage)(struct file *, struct page *);
int (*writepages)(struct address_space *, struct writeback_control *);
int (*set_page_dirty)(struct page *page);
+ void (*readahead)(struct readahead_control *);
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
@@ -781,12 +782,26 @@ cache in your filesystem. The following members are defined:
If defined, it should set the PageDirty flag, and the
PAGECACHE_TAG_DIRTY tag in the radix tree.
+``readahead``
+ Called by the VM to read pages associated with the address_space
+ object. The pages are consecutive in the page cache and are
+ locked. The implementation should decrement the page refcount
+ after starting I/O on each page. Usually the page will be
+ unlocked by the I/O completion handler. If the filesystem decides
+ to stop attempting I/O before reaching the end of the readahead
+ window, it can simply return. The caller will decrement the page
+ refcount and unlock the remaining pages for you. Set PageUptodate
+ if the I/O completes successfully. Setting PageError on any page
+ will be ignored; simply unlock the page if an I/O error occurs.
+
``readpages``
called by the VM to read pages associated with the address_space
object. This is essentially just a vector version of readpage.
Instead of just one page, several pages are requested.
readpages is only used for read-ahead, so read errors are
ignored. If anything goes wrong, feel free to give up.
+ This interface is deprecated and will be removed by the end of
+ 2020; implement readahead instead.
``write_begin``
Called by the generic buffered write code to ask the filesystem