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RE: [PATCH v2 2/10] xfs: Add support FALLOC_FL_INSERT_RANGE for fallocat

To: 'Brian Foster' <bfoster@xxxxxxxxxx>
Subject: RE: [PATCH v2 2/10] xfs: Add support FALLOC_FL_INSERT_RANGE for fallocate
From: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
Date: Mon, 12 May 2014 18:42:37 +0900
Cc: 'Dave Chinner' <david@xxxxxxxxxxxxx>, 'Theodore Ts'o' <tytso@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, 'linux-ext4' <linux-ext4@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, 'Ashish Sangwan' <a.sangwan@xxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
Dlp-filter: Pass
In-reply-to: <20140509152440.GA32489@xxxxxxxxxxxxxx>
References: <003801cf6aa7$f1f87b70$d5e97250$@samsung.com> <20140509152440.GA32489@xxxxxxxxxxxxxx>
Thread-index: AQI8l/c+50jbPyrOUhhBFU208NvpTgGlw03dmlUskyA=
> > +xfs_bmap_split_extent(
> > +   struct xfs_inode        *ip,
> > +   xfs_fileoff_t           split_fsb,
> > +   xfs_extnum_t            *split_ext)
> > +{
> > +   struct xfs_mount        *mp = ip->i_mount;
> > +   struct xfs_trans        *tp;
> > +   struct xfs_bmap_free    free_list;
> > +   xfs_fsblock_t           firstfsb;
> > +   int                     committed;
> > +   int                     error;
> > +
> > +   tp = xfs_trans_alloc(mp, XFS_TRANS_DIOSTRAT);
> > +   error = xfs_trans_reserve(tp, &M_RES(mp)->tr_write,
> > +                   XFS_DIOSTRAT_SPACE_RES(mp, 0), 0);
> > +
> > +   if (error) {
> > +           /*
> > +            * Free the transaction structure.
> > +            */
> > +           ASSERT(XFS_FORCED_SHUTDOWN(mp));
> 
Hi, Brian.
> As in the other patch, we're attempting to reserve fs blocks for the
> transaction, so ENOSPC is a possibility that I think the assert should
> accommodate.
How about removing the ASSERT completely as suggessted by Dave
in other thread?

> 
> > +           xfs_trans_cancel(tp, 0);
> > +           return error;
> > +   }
> > +

> > +
> > +           /*
> > +            * Before shifting extent into hole, make sure that the hole
> > +            * is large enough to accomodate the shift. This checking has
> > +            * to be performed for all except the last extent.
> > +            */
> > +           last_extent = (ifp->if_bytes / sizeof(xfs_bmbt_rec_t)) - 1;
> > +           if (last_extent != *current_ext) {
> > +                   xfs_bmbt_get_all(xfs_iext_get_ext(ifp,
> > +                                           *current_ext + 1), &right);
> > +                   if (startoff + got.br_blockcount > right.br_startoff) {
> > +                           error = XFS_ERROR(EINVAL);
> > +                           if (error)
> > +                                   goto del_cursor;
> > +                   }
> > +           }
> > +
> > +           /* Check if we can merge 2 adjacent extents */
> > +           if (last_extent != *current_ext &&
> > +               right.br_startoff == startoff + got.br_blockcount &&
> > +               right.br_startblock ==
> > +                           got.br_startblock + got.br_blockcount &&
> > +               right.br_state == got.br_state &&
> > +               right.br_blockcount + got.br_blockcount <= MAXEXTLEN) {
> > +                   blockcount = right.br_blockcount + got.br_blockcount;
> > +
> > +                   /* Make cursor point to the extent we will update */
> 
> The comment could be more clear about what we're doing in this case. For
> example:
> 
> /*
>  * Merge the current extent with the extent to the right. Remove the right
>  * extent, calculate a new block count for the current extent to cover the 
> range
>  * of both and decrement the number of extents in the fork.
>  */
> 
> I'd also move the comment before the blockcount calculation.
okay, I will add it as your suggestion.
> 
> > +                   if (cur) {
> > +                           error = xfs_bmbt_lookup_eq(cur,
> > +                                                      right.br_startoff,
> > +                                                      right.br_startblock,
> > +                                                      right.br_blockcount,
> > +                                                      &i);
> > +                           if (error)
> > +                                   goto del_cursor;
> > +                           XFS_WANT_CORRUPTED_GOTO(i == 1, del_cursor);
> > +                   }
> > +
> > +                   xfs_iext_remove(ip, *current_ext + 1, 1, 0);
> > +                   if (cur) {
> > +                           error = xfs_btree_delete(cur, &i);
> > +                           if (error)
> > +                                   goto del_cursor;
> > +                           XFS_WANT_CORRUPTED_GOTO(i == 1, del_cursor);
> > +                   }
> > +                   XFS_IFORK_NEXT_SET(ip, whichfork,
> > +                                   XFS_IFORK_NEXTENTS(ip, whichfork) - 1);
> > +
> > +           }
> > +
> > +           if (cur) {
> > +                   error = xfs_bmbt_lookup_eq(cur, got.br_startoff,
> > +                                              got.br_startblock,
> > +                                              got.br_blockcount,
> > +                                              &i);
> > +                   if (error)
> > +                           goto del_cursor;
> > +                   XFS_WANT_CORRUPTED_GOTO(i == 1, del_cursor);
> > +           }
> > +
> > +           if (got.br_blockcount < blockcount) {
> > +                   xfs_bmbt_set_blockcount(gotp, blockcount);
> > +                   got.br_blockcount = blockcount;
> > +           }
> 
> How about just 'if (blockcount)' so the algorithm is clear?
yes, more clear.
> 
> > +
> > +
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 97855c5..392b029 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -760,7 +760,8 @@ xfs_file_fallocate(
> >     if (!S_ISREG(inode->i_mode))
> >             return -EINVAL;
> >     if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
> > -                FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE))
> > +                FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
> > +                FALLOC_FL_INSERT_RANGE))
> >             return -EOPNOTSUPP;
> >
> >     xfs_ilock(ip, XFS_IOLOCK_EXCL);
> > @@ -790,6 +791,40 @@ xfs_file_fallocate(
> >             error = xfs_collapse_file_space(ip, offset, len);
> >             if (error)
> >                     goto out_unlock;
> > +   } else if (mode & FALLOC_FL_INSERT_RANGE) {
> > +           unsigned blksize_mask = (1 << inode->i_blkbits) - 1;
> > +           struct iattr iattr;
> > +
> > +           if (offset & blksize_mask || len & blksize_mask) {
> > +                   error = -EINVAL;
> > +                   goto out_unlock;
> > +           }
> > +
> > +           /* Check for wrap through zero */
> > +           if (inode->i_size + len > inode->i_sb->s_maxbytes) {
> > +                   error = -EFBIG;
> > +                   goto out_unlock;
> > +           }
> > +
> > +           /* Offset should be less than i_size */
> > +           if (offset >= i_size_read(inode)) {
> > +                   error = -EINVAL;
> > +                   goto out_unlock;
> > +           }
> > +
> > +           /*
> > +            * The first thing we do is to expand file to
> > +            * avoid data loss if there is error while shifting
> > +            */
> > +           iattr.ia_valid = ATTR_SIZE;
> > +           iattr.ia_size = i_size_read(inode) + len;
> > +           error = xfs_setattr_size(ip, &iattr);
> > +           if (error)
> > +                   goto out_unlock;
> 
> I don't necessarily know that it's problematic to do the setattr before
> the bmap fixup. We'll have a chance for partial completion of this
> operation either way. But I'm not a fan of the code duplication here.
> This also still skips the time update in the event of insert space
> failure, though perhaps that's not such a big deal if we're returning an
> error.
> 
> I think it would be better to leave things organized as before and
> introduce an error2 variable and a &nrshifts or some such parameter to
> xfs_insert_file_space() that initializes to 0 and returns the number of
> record shifts. The caller can then decide whether it's appropriate to
> break out immediately or do the inode size update and return the error.
> 
> Perhaps not the cleanest thing in the world, but also not the first
> place we would use 'error2' to manage error priorities (grep around for
> it)...
Yes, Right. I also thought such sequence at first. But we should consider
sudden power off and unplug device case during shifting extent.
While we are in the middle of shifitng extents and if there is sudden
power failure user can still think that data is lost as we won't get any
chance to update the file size in these cases.
Updating file size before the shifitng operation can start will prevent this.

Thanks.
> 
> Brian
> 
> > +
> > +           error = xfs_insert_file_space(ip, offset, len);
> > +           if (error)
> > +                   goto out_unlock;
> >     } else {
> >             if (!(mode & FALLOC_FL_KEEP_SIZE) &&
> >                 offset + len > i_size_read(inode)) {

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