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Message-ID: <20240930164402.GR21853@frogsfrogsfrogs>
Date: Mon, 30 Sep 2024 09:44:02 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, brauner@...nel.org, viro@...iv.linux.org.uk,
jack@...e.cz, dchinner@...hat.com, hch@....de, cem@...nel.org,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
hare@...e.de, martin.petersen@...cle.com,
catherine.hoang@...cle.com, mcgrof@...nel.org,
ritesh.list@...il.com, ojaswin@...ux.ibm.com
Subject: Re: [PATCH v6 4/7] xfs: Support FS_XFLAG_ATOMICWRITES
On Mon, Sep 30, 2024 at 09:03:49AM -0700, Darrick J. Wong wrote:
> On Mon, Sep 30, 2024 at 12:54:35PM +0000, John Garry wrote:
> > Add initial support for new flag FS_XFLAG_ATOMICWRITES.
> >
> > This flag is a file attribute that mirrors an ondisk inode flag. Actual
> > support for untorn file writes (for now) depends on both the iflag and the
> > underlying storage devices, which we can only really check at statx and
> > pwritev2() time. This is the same story as FS_XFLAG_DAX, which signals to
> > the fs that we should try to enable the fsdax IO path on the file (instead
> > of the regular page cache), but applications have to query STAT_ATTR_DAX to
> > find out if they really got that IO path.
> >
> > Current kernel support for atomic writes is based on HW support (for atomic
> > writes). Since for regular files XFS has no way to specify extent alignment
> > or granularity, atomic write size is limited to the FS block size.
> >
> > Signed-off-by: John Garry <john.g.garry@...cle.com>
> > ---
> > fs/xfs/libxfs/xfs_format.h | 11 ++++++++--
> > fs/xfs/libxfs/xfs_inode_buf.c | 38 ++++++++++++++++++++++++++++++++++
> > fs/xfs/libxfs/xfs_inode_util.c | 6 ++++++
> > fs/xfs/libxfs/xfs_sb.c | 2 ++
> > fs/xfs/xfs_buf.c | 15 +++++++++++++-
> > fs/xfs/xfs_buf.h | 5 ++++-
> > fs/xfs/xfs_buf_mem.c | 2 +-
> > fs/xfs/xfs_inode.h | 5 +++++
> > fs/xfs/xfs_ioctl.c | 37 +++++++++++++++++++++++++++++++++
> > fs/xfs/xfs_mount.h | 2 ++
> > fs/xfs/xfs_reflink.c | 4 ++++
> > fs/xfs/xfs_super.c | 4 ++++
> > include/uapi/linux/fs.h | 1 +
> > 13 files changed, 127 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> > index e1bfee0c3b1a..ed5e5442f0d4 100644
> > --- a/fs/xfs/libxfs/xfs_format.h
> > +++ b/fs/xfs/libxfs/xfs_format.h
> > @@ -352,11 +352,15 @@ xfs_sb_has_compat_feature(
> > #define XFS_SB_FEAT_RO_COMPAT_RMAPBT (1 << 1) /* reverse map btree */
> > #define XFS_SB_FEAT_RO_COMPAT_REFLINK (1 << 2) /* reflinked files */
> > #define XFS_SB_FEAT_RO_COMPAT_INOBTCNT (1 << 3) /* inobt block counts */
> > +#define XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES (1 << 31) /* atomicwrites enabled */
> > +
> > #define XFS_SB_FEAT_RO_COMPAT_ALL \
> > (XFS_SB_FEAT_RO_COMPAT_FINOBT | \
> > XFS_SB_FEAT_RO_COMPAT_RMAPBT | \
> > XFS_SB_FEAT_RO_COMPAT_REFLINK| \
> > - XFS_SB_FEAT_RO_COMPAT_INOBTCNT)
> > + XFS_SB_FEAT_RO_COMPAT_INOBTCNT | \
> > + XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES)
> > +
> > #define XFS_SB_FEAT_RO_COMPAT_UNKNOWN ~XFS_SB_FEAT_RO_COMPAT_ALL
> > static inline bool
> > xfs_sb_has_ro_compat_feature(
> > @@ -1093,16 +1097,19 @@ static inline void xfs_dinode_put_rdev(struct xfs_dinode *dip, xfs_dev_t rdev)
> > #define XFS_DIFLAG2_COWEXTSIZE_BIT 2 /* copy on write extent size hint */
> > #define XFS_DIFLAG2_BIGTIME_BIT 3 /* big timestamps */
> > #define XFS_DIFLAG2_NREXT64_BIT 4 /* large extent counters */
> > +#define XFS_DIFLAG2_ATOMICWRITES_BIT 5 /* atomic writes permitted */
> >
> > #define XFS_DIFLAG2_DAX (1 << XFS_DIFLAG2_DAX_BIT)
> > #define XFS_DIFLAG2_REFLINK (1 << XFS_DIFLAG2_REFLINK_BIT)
> > #define XFS_DIFLAG2_COWEXTSIZE (1 << XFS_DIFLAG2_COWEXTSIZE_BIT)
> > #define XFS_DIFLAG2_BIGTIME (1 << XFS_DIFLAG2_BIGTIME_BIT)
> > #define XFS_DIFLAG2_NREXT64 (1 << XFS_DIFLAG2_NREXT64_BIT)
> > +#define XFS_DIFLAG2_ATOMICWRITES (1 << XFS_DIFLAG2_ATOMICWRITES_BIT)
> >
> > #define XFS_DIFLAG2_ANY \
> > (XFS_DIFLAG2_DAX | XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE | \
> > - XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64)
> > + XFS_DIFLAG2_BIGTIME | XFS_DIFLAG2_NREXT64 | \
> > + XFS_DIFLAG2_ATOMICWRITES)
> >
> > static inline bool xfs_dinode_has_bigtime(const struct xfs_dinode *dip)
> > {
> > diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> > index 79babeac9d75..1e852cdd1d6f 100644
> > --- a/fs/xfs/libxfs/xfs_inode_buf.c
> > +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> > @@ -483,6 +483,36 @@ xfs_dinode_verify_nrext64(
> > return NULL;
> > }
> >
> > +static xfs_failaddr_t
> > +xfs_inode_validate_atomicwrites(
> > + struct xfs_mount *mp,
> > + uint32_t cowextsize,
> > + uint16_t mode,
> > + int64_t flags2)
> > +{
> > + /* superblock rocompat feature flag */
> > + if (!xfs_has_atomicwrites(mp))
> > + return __this_address;
> > +
> > + /* Only regular files and directories */
> > + if (!S_ISREG(mode) && !(S_ISDIR(mode)))
> > + return __this_address;
> > +
> > + /* COW extsize disallowed */
> > + if (flags2 & XFS_DIFLAG2_COWEXTSIZE)
> > + return __this_address;
> > +
> > + /* cowextsize must be zero */
> > + if (cowextsize)
> > + return __this_address;
> > +
> > + /* reflink is disallowed */
> > + if (flags2 & XFS_DIFLAG2_REFLINK)
> > + return __this_address;
>
> If we're only allowing atomic writes that are 1 fsblock or less, then
> copy on write will work correctly because CoWs are always done with
> fsblock granularity. The ioend remap is also committed atomically.
>
> IOWs, it's forcealign that isn't compatible with reflink and you can
> drop this incompatibility.
Also, why do you need to check cowextsize? I thought cowextsize==0 is a
requirement of forcealign (because everything is keyed off extsize) and
is not something that atomicwrites itself requires?
Same applies to xfs_ioctl_setattr_atomicwrites.
--D
> > +
> > + return NULL;
> > +}
> > +
> > xfs_failaddr_t
> > xfs_dinode_verify(
> > struct xfs_mount *mp,
> > @@ -663,6 +693,14 @@ xfs_dinode_verify(
> > !xfs_has_bigtime(mp))
> > return __this_address;
> >
> > + if (flags2 & XFS_DIFLAG2_ATOMICWRITES) {
> > + fa = xfs_inode_validate_atomicwrites(mp,
> > + be32_to_cpu(dip->di_cowextsize),
>
> Technically speaking, the space used by di_cowextsize isn't defined on
> !reflink filesystems. The contents are supposed to be zero, but nobody
> actually checks that, so you might want to special case this:
>
> fa = xfs_inode_validate_atomicwrites(mp,
> xfs_has_reflink(mp) ?
> be32_to_cpu(dip->di_cowextsize) : 0,
> mode, flags2);
>
> (inasmuch as this code is getting ugly and maybe you want to use a
> temporary variable)
>
> > + mode, flags2);
> > + if (fa)
> > + return fa;
> > + }
> > +
> > return NULL;
> > }
> >
> > diff --git a/fs/xfs/libxfs/xfs_inode_util.c b/fs/xfs/libxfs/xfs_inode_util.c
> > index cc38e1c3c3e1..e59e98783bf7 100644
> > --- a/fs/xfs/libxfs/xfs_inode_util.c
> > +++ b/fs/xfs/libxfs/xfs_inode_util.c
> > @@ -80,6 +80,8 @@ xfs_flags2diflags2(
> > di_flags2 |= XFS_DIFLAG2_DAX;
> > if (xflags & FS_XFLAG_COWEXTSIZE)
> > di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
> > + if (xflags & FS_XFLAG_ATOMICWRITES)
> > + di_flags2 |= XFS_DIFLAG2_ATOMICWRITES;
> >
> > return di_flags2;
> > }
> > @@ -126,6 +128,8 @@ xfs_ip2xflags(
> > flags |= FS_XFLAG_DAX;
> > if (ip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE)
> > flags |= FS_XFLAG_COWEXTSIZE;
> > + if (ip->i_diflags2 & XFS_DIFLAG2_ATOMICWRITES)
> > + flags |= FS_XFLAG_ATOMICWRITES;
> > }
> >
> > if (xfs_inode_has_attr_fork(ip))
> > @@ -224,6 +228,8 @@ xfs_inode_inherit_flags2(
> > }
> > if (pip->i_diflags2 & XFS_DIFLAG2_DAX)
> > ip->i_diflags2 |= XFS_DIFLAG2_DAX;
> > + if (pip->i_diflags2 & XFS_DIFLAG2_ATOMICWRITES)
> > + ip->i_diflags2 |= XFS_DIFLAG2_ATOMICWRITES;
> >
> > /* Don't let invalid cowextsize hints propagate. */
> > failaddr = xfs_inode_validate_cowextsize(ip->i_mount, ip->i_cowextsize,
> > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > index d95409f3cba6..dd819561d0a5 100644
> > --- a/fs/xfs/libxfs/xfs_sb.c
> > +++ b/fs/xfs/libxfs/xfs_sb.c
> > @@ -164,6 +164,8 @@ xfs_sb_version_to_features(
> > features |= XFS_FEAT_REFLINK;
> > if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_INOBTCNT)
> > features |= XFS_FEAT_INOBTCNT;
> > + if (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_ATOMICWRITES)
> > + features |= XFS_FEAT_ATOMICWRITES;
> > if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_FTYPE)
> > features |= XFS_FEAT_FTYPE;
> > if (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_SPINODES)
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index aa4dbda7b536..44bee3e2b2bb 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -2060,6 +2060,8 @@ int
> > xfs_init_buftarg(
> > struct xfs_buftarg *btp,
> > size_t logical_sectorsize,
> > + unsigned int awu_min,
> > + unsigned int awu_max,
> > const char *descr)
> > {
> > /* Set up device logical sector size mask */
> > @@ -2086,6 +2088,9 @@ xfs_init_buftarg(
> > btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
> > btp->bt_shrinker->private_data = btp;
> > shrinker_register(btp->bt_shrinker);
> > +
> > + btp->bt_bdev_awu_min = awu_min;
> > + btp->bt_bdev_awu_max = awu_max;
> > return 0;
> >
> > out_destroy_io_count:
> > @@ -2102,6 +2107,7 @@ xfs_alloc_buftarg(
> > {
> > struct xfs_buftarg *btp;
> > const struct dax_holder_operations *ops = NULL;
> > + unsigned int awu_min = 0, awu_max = 0;
> >
> > #if defined(CONFIG_FS_DAX) && defined(CONFIG_MEMORY_FAILURE)
> > ops = &xfs_dax_holder_operations;
> > @@ -2115,6 +2121,13 @@ xfs_alloc_buftarg(
> > btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
> > mp, ops);
> >
> > + if (bdev_can_atomic_write(btp->bt_bdev)) {
> > + struct request_queue *q = bdev_get_queue(btp->bt_bdev);
> > +
> > + awu_min = queue_atomic_write_unit_min_bytes(q);
> > + awu_max = queue_atomic_write_unit_max_bytes(q);
> > + }
> > +
> > /*
> > * When allocating the buftargs we have not yet read the super block and
> > * thus don't know the file system sector size yet.
> > @@ -2122,7 +2135,7 @@ xfs_alloc_buftarg(
> > if (xfs_setsize_buftarg(btp, bdev_logical_block_size(btp->bt_bdev)))
> > goto error_free;
> > if (xfs_init_buftarg(btp, bdev_logical_block_size(btp->bt_bdev),
> > - mp->m_super->s_id))
> > + awu_min, awu_max, mp->m_super->s_id))
> > goto error_free;
>
> Rather than passing this into the constructor and making the xmbuf code
> pass zeroes, why not set the awu values here in xfs_alloc_buftarg just
> before returning btp?
>
> if (bdev_can_atomic_write(btp->bt_bdev)) {
> struct request_queue *q = bdev_get_queue(btp->bt_bdev);
>
> btp->bt_bdev_awu_min = queue_atomic_write_unit_min_bytes(q);
> btp->bt_bdev_awu_max = queue_atomic_write_unit_max_bytes(q);
> }
>
>
> --D
>
> > return btp;
> > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> > index 209a389f2abc..b813cb60a8f3 100644
> > --- a/fs/xfs/xfs_buf.h
> > +++ b/fs/xfs/xfs_buf.h
> > @@ -124,6 +124,9 @@ struct xfs_buftarg {
> > struct percpu_counter bt_io_count;
> > struct ratelimit_state bt_ioerror_rl;
> >
> > + /* Atomic write unit values */
> > + unsigned int bt_bdev_awu_min, bt_bdev_awu_max;
> > +
> > /* built-in cache, if we're not using the perag one */
> > struct xfs_buf_cache bt_cache[];
> > };
> > @@ -393,7 +396,7 @@ bool xfs_verify_magic16(struct xfs_buf *bp, __be16 dmagic);
> >
> > /* for xfs_buf_mem.c only: */
> > int xfs_init_buftarg(struct xfs_buftarg *btp, size_t logical_sectorsize,
> > - const char *descr);
> > + unsigned int awu_min, unsigned int awu_max, const char *descr);
> > void xfs_destroy_buftarg(struct xfs_buftarg *btp);
> >
> > #endif /* __XFS_BUF_H__ */
> > diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> > index 07bebbfb16ee..722d75f89767 100644
> > --- a/fs/xfs/xfs_buf_mem.c
> > +++ b/fs/xfs/xfs_buf_mem.c
> > @@ -93,7 +93,7 @@ xmbuf_alloc(
> > btp->bt_meta_sectorsize = XMBUF_BLOCKSIZE;
> > btp->bt_meta_sectormask = XMBUF_BLOCKSIZE - 1;
> >
> > - error = xfs_init_buftarg(btp, XMBUF_BLOCKSIZE, descr);
> > + error = xfs_init_buftarg(btp, XMBUF_BLOCKSIZE, 0, 0, descr);
> > if (error)
> > goto out_bcache;
> >
> > diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> > index 97ed912306fd..1c62ee294a5a 100644
> > --- a/fs/xfs/xfs_inode.h
> > +++ b/fs/xfs/xfs_inode.h
> > @@ -327,6 +327,11 @@ static inline bool xfs_inode_has_bigrtalloc(struct xfs_inode *ip)
> > (XFS_IS_REALTIME_INODE(ip) ? \
> > (ip)->i_mount->m_rtdev_targp : (ip)->i_mount->m_ddev_targp)
> >
> > +static inline bool xfs_inode_has_atomicwrites(struct xfs_inode *ip)
> > +{
> > + return ip->i_diflags2 & XFS_DIFLAG2_ATOMICWRITES;
> > +}
> > +
> > /*
> > * In-core inode flags.
> > */
> > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > index a20d426ef021..81872c32dcb2 100644
> > --- a/fs/xfs/xfs_ioctl.c
> > +++ b/fs/xfs/xfs_ioctl.c
> > @@ -469,6 +469,36 @@ xfs_fileattr_get(
> > return 0;
> > }
> >
> > +static int
> > +xfs_ioctl_setattr_atomicwrites(
> > + struct xfs_inode *ip,
> > + struct fileattr *fa)
> > +{
> > + struct xfs_buftarg *target = xfs_inode_buftarg(ip);
> > + struct xfs_mount *mp = ip->i_mount;
> > + struct xfs_sb *sbp = &mp->m_sb;
> > +
> > + if (!xfs_has_atomicwrites(mp))
> > + return -EINVAL;
> > +
> > + if (target->bt_bdev_awu_min > sbp->sb_blocksize)
> > + return -EINVAL;
> > +
> > + if (target->bt_bdev_awu_max < sbp->sb_blocksize)
> > + return -EINVAL;
> > +
> > + if (xfs_is_reflink_inode(ip))
> > + return -EINVAL;
> > +
> > + if (fa->fsx_xflags & FS_XFLAG_COWEXTSIZE)
> > + return -EINVAL;
> > +
> > + if (fa->fsx_cowextsize)
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +
> > static int
> > xfs_ioctl_setattr_xflags(
> > struct xfs_trans *tp,
> > @@ -478,6 +508,7 @@ xfs_ioctl_setattr_xflags(
> > struct xfs_mount *mp = ip->i_mount;
> > bool rtflag = (fa->fsx_xflags & FS_XFLAG_REALTIME);
> > uint64_t i_flags2;
> > + int error;
> >
> > if (rtflag != XFS_IS_REALTIME_INODE(ip)) {
> > /* Can't change realtime flag if any extents are allocated. */
> > @@ -512,6 +543,12 @@ xfs_ioctl_setattr_xflags(
> > if (i_flags2 && !xfs_has_v3inodes(mp))
> > return -EINVAL;
> >
> > + if (fa->fsx_xflags & FS_XFLAG_ATOMICWRITES) {
> > + error = xfs_ioctl_setattr_atomicwrites(ip, fa);
> > + if (error)
> > + return error;
> > + }
> > +
> > ip->i_diflags = xfs_flags2diflags(ip, fa->fsx_xflags);
> > ip->i_diflags2 = i_flags2;
> >
> > diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> > index 96496f39f551..6ac6518a2ef3 100644
> > --- a/fs/xfs/xfs_mount.h
> > +++ b/fs/xfs/xfs_mount.h
> > @@ -298,6 +298,7 @@ typedef struct xfs_mount {
> > #define XFS_FEAT_NEEDSREPAIR (1ULL << 25) /* needs xfs_repair */
> > #define XFS_FEAT_NREXT64 (1ULL << 26) /* large extent counters */
> > #define XFS_FEAT_EXCHANGE_RANGE (1ULL << 27) /* exchange range */
> > +#define XFS_FEAT_ATOMICWRITES (1ULL << 28) /* atomic writes support */
> >
> > /* Mount features */
> > #define XFS_FEAT_NOATTR2 (1ULL << 48) /* disable attr2 creation */
> > @@ -384,6 +385,7 @@ __XFS_ADD_V4_FEAT(projid32, PROJID32)
> > __XFS_HAS_V4_FEAT(v3inodes, V3INODES)
> > __XFS_HAS_V4_FEAT(crc, CRC)
> > __XFS_HAS_V4_FEAT(pquotino, PQUOTINO)
> > +__XFS_HAS_FEAT(atomicwrites, ATOMICWRITES)
> >
> > /*
> > * Mount features
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index 6fde6ec8092f..6679b12a56c9 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -1471,6 +1471,10 @@ xfs_reflink_remap_prep(
> > if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
> > goto out_unlock;
> >
> > + /* Don't reflink atomic write inodes */
> > + if (xfs_inode_has_atomicwrites(src) || xfs_inode_has_atomicwrites(dest))
> > + goto out_unlock;
> > +
> > /* Don't share DAX file data with non-DAX file. */
> > if (IS_DAX(inode_in) != IS_DAX(inode_out))
> > goto out_unlock;
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index fbb3a1594c0d..97c1d9493cdb 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -1733,6 +1733,10 @@ xfs_fs_fill_super(
> > mp->m_features &= ~XFS_FEAT_DISCARD;
> > }
> >
> > + if (xfs_has_atomicwrites(mp))
> > + xfs_warn(mp,
> > + "EXPERIMENTAL atomicwrites feature in use. Use at your own risk!");
> > +
> > if (xfs_has_reflink(mp)) {
> > if (mp->m_sb.sb_rblocks) {
> > xfs_alert(mp,
> > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > index 753971770733..e813217e0fe4 100644
> > --- a/include/uapi/linux/fs.h
> > +++ b/include/uapi/linux/fs.h
> > @@ -158,6 +158,7 @@ struct fsxattr {
> > #define FS_XFLAG_FILESTREAM 0x00004000 /* use filestream allocator */
> > #define FS_XFLAG_DAX 0x00008000 /* use DAX for IO */
> > #define FS_XFLAG_COWEXTSIZE 0x00010000 /* CoW extent size allocator hint */
> > +#define FS_XFLAG_ATOMICWRITES 0x00020000 /* atomic writes enabled */
> > #define FS_XFLAG_HASATTR 0x80000000 /* no DIFLAG for this */
> >
> > /* the read-only stuff doesn't really belong here, but any other place is
> > --
> > 2.31.1
> >
> >
>
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