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Re: [RFC PATCH 2/4] xfs: add xfs_create_tmpfile() for O_TMPFILE support

To: Zhi Yong Wu <zwu.kernel@xxxxxxxxx>
Subject: Re: [RFC PATCH 2/4] xfs: add xfs_create_tmpfile() for O_TMPFILE support
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 26 Nov 2013 08:36:01 +1100
Cc: xfs@xxxxxxxxxxx, Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1385379154-3802-3-git-send-email-zwu.kernel@xxxxxxxxx>
References: <1385379154-3802-1-git-send-email-zwu.kernel@xxxxxxxxx> <1385379154-3802-3-git-send-email-zwu.kernel@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Nov 25, 2013 at 07:32:32PM +0800, Zhi Yong Wu wrote:
> From: Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx>
> 
> The function is used to create one O_TMPFILE file.
> 
> http://oss.sgi.com/archives/xfs/2013-08/msg00339.html
> 
> Signed-off-by: Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx>
> ---
>  fs/xfs/xfs_inode.c       |  129 
> ++++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_inode.h       |    2 +
>  fs/xfs/xfs_shared.h      |    4 +-
>  fs/xfs/xfs_trans_resv.c  |   35 ++++++++++++
>  fs/xfs/xfs_trans_resv.h  |    2 +
>  fs/xfs/xfs_trans_space.h |    2 +
>  6 files changed, 173 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 1c23bdf..e1832de 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1337,6 +1337,135 @@ xfs_create(
>  }
>  
>  int
> +xfs_create_tmpfile(
> +     xfs_mount_t             *mp,
> +     umode_t                 mode,
> +     dev_t                   rdev,
> +     xfs_inode_t             **ipp)
> +{
> +     struct xfs_inode        *ip = NULL;
> +     struct xfs_trans        *tp = NULL;
> +     int                     error;
> +     uint                    cancel_flags = XFS_TRANS_RELEASE_LOG_RES;
> +     struct xfs_dquot        *udqp = NULL;
> +     struct xfs_dquot        *gdqp = NULL;
> +     struct xfs_dquot        *pdqp = NULL;
> +     struct xfs_trans_res    *tres;
> +     uint                    resblks;
> +
> +     if (XFS_FORCED_SHUTDOWN(mp))
> +             return XFS_ERROR(EIO);
> +
> +     /*
> +      * Make sure that we have allocated dquot(s) on disk.
> +      */
> +     error = xfs_qm_vop_dqalloc(NULL, mp, xfs_kuid_to_uid(current_fsuid()),
> +                                     xfs_kgid_to_gid(current_fsgid()),
> +                                     XFS_PROJID_DEFAULT,
> +                                     XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
> +                                     &udqp, &gdqp, &pdqp);
> +     if (error)
> +             return error;

Is XFS_PROJID_DEFAULT correct here? If we are getting a parent inode
from ->tmpfile, then this should be handled the same way as for
xfs_create.

> +
> +     resblks = XFS_CREATE_TMPFILE_SPACE_RES(mp);
> +     tp = xfs_trans_alloc(mp, XFS_TRANS_CREATE_TMPFILE);
> +
> +     /*
> +      * Initially assume that the file does not exist and
> +      * reserve the resources for that case.  If that is not
> +      * the case we'll drop the one we have and get a more
> +      * appropriate transaction later.
> +      */
> +     tres = &M_RES(mp)->tr_create_tmpfile;
> +     error = xfs_trans_reserve(tp, tres, resblks, 0);
> +     if (error == ENOSPC) {
> +             /* flush outstanding delalloc blocks and retry */
> +             xfs_flush_inodes(mp);
> +             error = xfs_trans_reserve(tp, tres, resblks, 0);
> +     }
> +     if (error == ENOSPC) {
> +             /* No space at all so try a "no-allocation" reservation */
> +             resblks = 0;
> +             error = xfs_trans_reserve(tp, tres, 0, 0);
> +     }
> +     if (error) {
> +             cancel_flags = 0;
> +             goto out_trans_cancel;
> +     }

I don't think this is necessary here. The ENOSPC flushing in
xfs_create() is done to ensure we have space for directory block
creation, not so much for inode allocation. Hence it doesn't make a
lot of sense to have this here....

> +     /*
> +      * Reserve disk quota and the inode.
> +      */
> +     error = xfs_trans_reserve_quota(tp, mp, udqp, gdqp,
> +                                             pdqp, resblks, 1, 0);
> +     if (error)
> +             goto out_trans_cancel;
> +
> +     /*
> +      * A newly created regular or special file just has one directory
> +      * entry pointing to them, but a directory also the "." entry
> +      * pointing to itself.
> +      */
> +     error = xfs_dir_ialloc(&tp, NULL, mode, 1, rdev,
> +                             XFS_PROJID_DEFAULT, resblks > 0,
> +                             &ip, NULL);
> +     if (error) {
> +             if (error == ENOSPC)
> +                     goto out_trans_cancel;
> +             goto out_trans_abort;
> +     }
> +
> +     /*
> +      * If this is a synchronous mount, make sure that the
> +      * create transaction goes to disk before returning to
> +      * the user.
> +      */
> +     if (mp->m_flags & (XFS_MOUNT_WSYNC|XFS_MOUNT_DIRSYNC))
> +             xfs_trans_set_sync(tp);

I'm not sure that XFS_MOUNT_DIRSYNC shoul dbe checked here, as there
is no directory operations to synchronise at all...

> +STATIC uint
> +xfs_calc_icreate_tmpfile_reservation(xfs_mount_t *mp)
> +{
> +     return XFS_DQUOT_LOGRES(mp) +
> +             xfs_calc_icreate_resv_alloc(mp) +
> +             xfs_calc_inode_res(mp, 1) +
> +             xfs_calc_buf_res(1, XFS_FSB_TO_B(mp, 1)) +
> +             xfs_calc_buf_res(2, mp->m_sb.sb_sectsize);
> +}
> +
> +STATIC uint
> +__xfs_calc_create_tmpfile_reservation(
> +     struct xfs_mount        *mp)
> +{
> +     return XFS_DQUOT_LOGRES(mp) +
> +             xfs_calc_create_resv_alloc(mp) +
> +             xfs_calc_inode_res(mp, 1) +
> +             xfs_calc_buf_res(1, XFS_FSB_TO_B(mp, 1)) +
> +             xfs_calc_buf_res(2, mp->m_sb.sb_sectsize);
> +}

What exactly is being modified here? All of the other reservations
have comments explaining what each of the individual components of
the reservation are. Yes, I can see that there's an inode, a
filesystem block and 2 sectors being reserved, but what are they?

It's also double counting the XFS_DQUOT_LOGRES(), as they are
accounted for in xfs_calc_[i]create_reservation().

Also, the directory create reservations are broken up into two
components - the inode allocation and the common directory name
creation component, and so the tmpfile reservation should probably
be broken up the same way. i.e this:

> +
> +STATIC uint
> +xfs_calc_create_tmpfile_reservation(
> +     struct xfs_mount        *mp)
> +{
> +     if (xfs_sb_version_hascrc(&mp->m_sb))
> +             return xfs_calc_icreate_tmpfile_reservation(mp);
> +     return __xfs_calc_create_tmpfile_reservation(mp);
> +}

Could simply be:

STATIC uint
xfs_calc_create_tmpfile_reservation(
        struct xfs_mount        *mp)
{
        uint    res;

        if (xfs_sb_version_hascrc(&mp->m_sb))
                res = xfs_calc_icreate_resv_alloc(mp);
        else
                res = xfs_calc_create_resv_alloc(mp);
        return res + xfs_calc_iunlink_add_resv(mp);
}


> diff --git a/fs/xfs/xfs_trans_space.h b/fs/xfs/xfs_trans_space.h
> index 7d2c920..16fba89 100644
> --- a/fs/xfs/xfs_trans_space.h
> +++ b/fs/xfs/xfs_trans_space.h
> @@ -61,6 +61,8 @@
>       (XFS_DAENTER_SPACE_RES(mp, XFS_ATTR_FORK) + XFS_B_TO_FSB(mp, v))
>  #define      XFS_CREATE_SPACE_RES(mp,nl)     \
>       (XFS_IALLOC_SPACE_RES(mp) + XFS_DIRENTER_SPACE_RES(mp,nl))
> +#define      XFS_CREATE_TMPFILE_SPACE_RES(mp)        \
> +     XFS_IALLOC_SPACE_RES(mp)

I wouldn't bother with this macro - just use XFS_IALLOC_SPACE_RES()
directly.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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