On 02/14/2017 01:43 AM, Christoph Hellwig wrote:
> On Mon, Feb 13, 2017 at 08:46:02PM -0600, Goldwyn Rodrigues wrote:
>> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> Please Cc the while series to all lists, otherwiwe it's impossible
> to review the thing.
>
>>
>> If IOCB_NONBLOCKING is set:
>> + Check if writing beyond end of file, if yes return EAGAIN
>> - check if writing to a hole which does not have allocated
>> file blocks.
>> - Check if i_rwsem is immediately lockable in xfs_rw_ilock()
>
> Why the + vs - above?
A mistake. It does not mean anything besides bullets.
>
>> -static inline void
>> +static inline int
>> xfs_rw_ilock(
>
> This function has been removed a while ago.
And thanks for putting in xfs_ilock_nowait(). This can't be done in a
cleaner way. I was very skeptical of adding yet another flag.
>
>>
>> + if (iocb->ki_flags & IOCB_NONBLOCKING) {
>> + struct xfs_bmbt_irec imap;
>> + xfs_fileoff_t offset_fsb, end_fsb;
>> + int nimaps = 1, ret = 0;
>> + end_fsb = XFS_B_TO_FSB(ip->i_mount, iocb->ki_pos + count);
>> + if (XFS_B_TO_FSB(ip->i_mount, i_size_read(inode)) < end_fsb)
>> + return -EAGAIN;
>
> Bogus check, XFS supports async write beyond EOF if the space is
> preallocated.
I assume this will be covered by xfs_bmapi_write().
>
>> + /* Check if it is an unallocated hole */
>> + offset_fsb = XFS_B_TO_FSBT(ip->i_mount, iocb->ki_pos);
>> +
>> + ret = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
>> + &nimaps, 0);
>> + if (ret)
>> + return ret;
>> + if (!nimaps || imap.br_startblock == HOLESTARTBLOCK)
>> + return -EAGAIN;
>
> This would need the ilock. But extent list lookups are expensive,
> so please don't add another one here. Just return when we hit the
> first unallocated extent in xfs_bmapi_write - either a short write or
> -EAGAIN if nothing has been written.
So in xfs_bmapi_write (and referring to), I would need a new flag, say
XFS_BMAPI_NOALLOC which would bail to error0, setting error=-EAGAIN if
need_alloc or was_delay is set. This flag XFS_BMAPI_NOALLOC is set in
xfs_iomap_write_direct(). I did not understand short writes. Where can I
get a short write?
If I understand correctly, we do add the flag.
>
>> error = xfs_break_layouts(inode, iolock, true);
>> if (error)
>> return error;
>
> Additionally this can drop the iolock, so you might get a new
> hole after it.
>
--
Goldwyn
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