vfs: make remap_file_range functions take and return bytes completed

Change the remap_file_range functions to take a number of bytes to
operate upon and return the number of bytes they operated on.  This is a
requirement for allowing fs implementations to return short clone/dedupe
results to the user, which will enable us to obey resource limits in a
graceful manner.

A subsequent patch will enable copy_file_range to signal to the
->clone_file_range implementation that it can handle a short length,
which will be returned in the function's return value.  For now the
short return is not implemented anywhere so the behavior won't change --
either copy_file_range manages to clone the entire range or it tries an
alternative.

Neither clone ioctl can take advantage of this, alas.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 6f5babfee27b..1bd2919deaca 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -883,9 +883,9 @@ struct file_operations {
         unsigned (*mmap_capabilities)(struct file *);
 #endif
         ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, unsigned int);
-        int (*remap_file_range)(struct file *file_in, loff_t pos_in,
-                                struct file *file_out, loff_t pos_out,
-                                u64 len, unsigned int remap_flags);
+        loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in,
+                                   struct file *file_out, loff_t pos_out,
+                                   loff_t len, unsigned int remap_flags);
         int (*fadvise)(struct file *, loff_t, loff_t, int);
 };
 
@@ -966,8 +966,8 @@ otherwise noted.
         implementation should remap len bytes at pos_in of the source file into
         the dest file at pos_out.  Implementations must handle callers passing
         in len == 0; this means "remap to the end of the source file".  The
-        return value should be zero if all bytes were remapped, or the usual
-        negative error code if the remapping did not succeed completely.
+        return value should the number of bytes remapped, or the usual
+        negative error code if errors occurred before any bytes were remapped.
         The remap_flags parameter accepts REMAP_FILE_* flags.  If
         REMAP_FILE_DEDUP is set then the implementation must only remap if the
         requested file ranges have identical contents.