On Sun, Jan 14, 2007 at 05:25:44PM +0300, Dmitriy Monakhov wrote:

Nick Piggin [off-list ref] writes:

quoted

If prepare_write fails with AOP_TRUNCATED_PAGE, or if commit_write fails, then
we may have failed the write operation despite prepare_write having
instantiated blocks past i_size. Fix this, and consolidate the trimming into
one place.

Signed-off-by: Nick Piggin <redacted>

Index: linux-2.6/mm/filemap.c
===================================================================

--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c

@@ -1911,22 +1911,9 @@ generic_file_buffered_write(struct kiocb
 		}
 
 		status = a_ops->prepare_write(file, page, offset, offset+bytes);
-		if (unlikely(status)) {
-			loff_t isize = i_size_read(inode);
+		if (unlikely(status))
+			goto fs_write_aop_error;

May be it's stupid question but still..
Why we treat non zero prepare_write() return code as error, it may be positive.
Positive error code may be used as fine grained 'bytes' limiter in case of 
blksize < pgsize as follows:

                status = a_ops->prepare_write(file, page, offset, offset+bytes);
		if (unlikely(status)) {
                        if (status > 0) {
                                bytes = min(bytes, status);
                                status = 0;
                        } else {
                	        goto fs_write_aop_error;
                        }
                }
---
This is useful because fs may want to reduce 'bytes' by number of reasons,
for example make it blksize bound. 
Example : filesystem has 1k blksize and only two free blocks. And we try 
write 4k bytes.
Currently  write(fd, buff, 4096) will return -ENOSPC
But after this fix write(fd, buff, 4096) will return as mutch as it can (2048).

It isn't a stupid question. Hmm, while it isn't documented in vfs.txt, it
seems like some filesystems actually do this. AFFS, maybe JFFS. So good
catch, thanks.

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