On Mon, Mar 12, 2007 at 11:55:30AM +0300, Dmitriy Monakhov wrote:
> Nick Piggin <[EMAIL PROTECTED]> writes:
>
> > On Mon, Mar 12, 2007 at 10:58:10AM +0300, Dmitriy Monakhov wrote:
> >> @@ -2240,6 +2241,29 @@ ssize_t generic_file_aio_write(struct kiocb *iocb,
> >> const struct iovec *iov,
> >> mutex_lock(&inode->i_mutex);
> >> ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
> >> &iocb->ki_pos);
> >> + /*
> >> + * If __generic_file_aio_write_nolock has failed.
> >> + * This may happen because of:
> >> + * 1) Bad segment found (failed before actual write attempt)
> >> + * 2) Segments are good, but actual write operation failed
> >> + * and may have instantiated a few blocks outside i_size.
> >> + * a) in case of buffered write these blocks was already
> >> + * trimmed by generic_file_buffered_write()
> >> + * b) in case of O_DIRECT these blocks weren't trimmed yet.
> >> + *
> >> + * In case of (2b) these blocks have to be trimmed off again.
> >> + */
> >> + if (unlikely( ret < 0 && file->f_flags & O_DIRECT)) {
> >> + unsigned long nr_segs_avail = nr_segs;
> >> + size_t count = 0;
> >> + if (!generic_segment_checks(iov, &nr_segs_avail, &count,
> >> + VERIFY_READ)) {
> >> + /*It is (2b) case, because segments are good*/
> >> + loff_t isize = i_size_read(inode);
> >> + if (pos + count > isize)
> >> + vmtruncate(inode, isize);
> >> + }
> >> + }
> >
> > OK, but wouldn't this be better to be done in the actual direct IO
> > functions themselves? Thus you could be sure that you have the 2b case,
> > and the code would be less fragile to something changing?
> Ohh, We can't just call vmtruncate() after generic_file_direct_write()
> failure while __generic_file_aio_write_nolock() becase where is no guarantee
> what i_mutex held. In fact all existing fs always invoke
> __generic_file_aio_write_nolock() with i_mutex held in case of S_ISREG files,
> but this was't explicitly demanded and documented. I've proposed to do it in
> previous versions of this patch, because it this just document current state
> of affairs, but David Chinner wasn't agree with it.
It seemed like it was documented in the comments that you altered in this
patch...
How would such a filesystem that did not hold i_mutex propose to fix the
problem?
The burden should be on those filesystems that might not want to hold
i_mutex here, to solve the problem nicely, rather than generic code to take
this ugly code.
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