On Sun, Jan 14, 2007 at 05:25:44PM +0300, Dmitriy Monakhov wrote:
> Nick Piggin <npiggin@xxxxxxx> writes:
>
> > 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 <npiggin@xxxxxxx>
> >
> > 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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