[patch 09/12] sendfile: several fixes

[akpm@linux-foundation.org]

From: Mandeep Singh Baines <msb@google.com>

Three fixes for sendfile, mostly related to sending large files from pseudo
filesystems:

- Fix sendfile for offsets > 300G. This can happen with pseudo filesystems.
  This happens because the overflow check is using inode->i_sb->s_maxbytes
  and not the superblock of the backing device's s_maxbytes. For a regular file
  these are interchangible but for a special file these are different and you
  want the latter.

- Don't compare against the max of the out_inode's superblock. Doesn't make
  sense.

- For pseudo and other filesystems with s_maxbytes set to ~0ULL, max ends up
  holding a negative number as it is signed. Check for and correct that.

Signed-off-by: Robert Love <rlove@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/read_write.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff -puN fs/read_write.c~sendfile-several-fixes fs/read_write.c
--- a/fs/read_write.c~sendfile-several-fixes
+++ a/fs/read_write.c
@@ -835,8 +835,15 @@ static ssize_t do_sendfile(int out_fd, i
 		goto fput_out;
 	count = retval;
 
-	if (!max)
-		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
+	if (!max) {
+		max = in_inode->i_mapping->host->i_sb->s_maxbytes;
+		/*
+		 * For psuedo filesystems, s_maxbytes is ~0ULL. When converted
+		 * to loff_t, it can go negative. So we check for and fix that.
+		 */
+		if (max < 0)
+			max = LLONG_MAX;
+	}
 
 	pos = *ppos;
 	retval = -EINVAL;
_