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From:   Filipe Manana <fdmanana@kernel.org>
Date:   Fri, 23 Sep 2022 16:32:30 +0100
Message-ID: <CAL3q7H540e8Rpxg5Rdv20OFueYhb4PPt2YQs5oZ82N8dciWx1A@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] btrfs: send: fix failures when processing inodes
 with no links
To:     bingjing chang <bxxxjxxg@gmail.com>
Cc:     bingjingc <bingjingc@synology.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>, Chris Mason <clm@fb.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Robbie Ko <robbieko@synology.com>, stable@vger.kernel.org
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On Fri, Sep 23, 2022 at 3:16 PM bingjing chang <bxxxjxxg@gmail.com> wrote:
>
> Filipe Manana <fdmanana@kernel.org> =E6=96=BC 2022=E5=B9=B49=E6=9C=8822=
=E6=97=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=886:08=E5=AF=AB=E9=81=93=EF=BC=
=9A
> >
> > ,
> >
> > On Fri, Aug 12, 2022 at 3:36 PM bingjing chang <bxxxjxxg@gmail.com> wro=
te:
> > >
> > > Filipe Manana <fdmanana@kernel.org> =E6=96=BC 2022=E5=B9=B48=E6=9C=88=
11=E6=97=A5 =E9=80=B1=E5=9B=9B =E6=99=9A=E4=B8=8A8:00=E5=AF=AB=E9=81=93=EF=
=BC=9A
> > > >
> > > > On Thu, Aug 11, 2022 at 11:09 AM bingjingc <bingjingc@synology.com>=
 wrote:
> > > > >
> > > > > From: BingJing Chang <bingjingc@synology.com>
> > > > >
> > > > > There is a bug causing send failures when processing an orphan di=
rectory
> > > > > with no links. In commit 46b2f4590aab ("Btrfs: fix send failure w=
hen root
> > > > > has deleted files still open")', the orphan inode issue was addre=
ssed. The
> > > > > send operation fails with a ENOENT error because of any attempts =
to
> > > > > generate a path for the inode with a link count of zero. Therefor=
e, in that
> > > > > patch, sctx->ignore_cur_inode was introduced to be set if the cur=
rent inode
> > > > > has a link count of zero for bypassing some unnecessary steps. An=
d a helper
> > > > > function btrfs_unlink_all_paths() was introduced and called to cl=
ean up old
> > > > > paths found in the parent snapshot. However, not only regular fil=
es but
> > > > > also directories can be orphan inodes. So if the send operation m=
eets an
> > > > > orphan directory, it will issue a wrong unlink command for that d=
irectory
> > > > > now. Soon the receive operation fails with a EISDIR error. Beside=
s, the
> > > > > send operation also fails with a ENOENT error later when it tries=
 to
> > > > > generate a path of it.
> > > > >
> > > > > Similar example but making an orphan dir for an incremental send:
> > > > >
> > > > >   $ btrfs subvolume create vol
> > > > >   $ mkdir vol/dir
> > > > >   $ touch vol/dir/foo
> > > > >
> > > > >   $ btrfs subvolume snapshot -r vol snap1
> > > > >   $ btrfs subvolume snapshot -r vol snap2
> > > > >
> > > > >   # Turn the second snapshot to RW mode and delete the whole dir =
while
> > > > >   # holding an open file descriptor on it.
> > > > >   $ btrfs property set snap2 ro false
> > > > >   $ exec 73<snap2/dir
> > > > >   $ rm -rf snap2/dir
> > > > >
> > > > >   # Set the second snapshot back to RO mode and do an incremental=
 send.
> > > > >   $ btrfs property set snap2 ro true
> > > > >   $ mkdir receive_dir
> > > > >   $ btrfs send snap2 -p snap1 | btrfs receive receive_dir/
> > > > >   At subvol snap2
> > > > >   At snapshot snap2
> > > > >   ERROR: send ioctl failed with -2: No such file or directory
> > > > >   ERROR: unlink dir failed. Is a directory
> > > > >
> > > > > Actually, orphan inodes are more common use cases in cascading ba=
ckups.
> > > > > (Please see the illustration below.) In a cascading backup, a use=
r wants
> > > > > to replicate a couple of snapshots from Machine A to Machine B an=
d from
> > > > > Machine B to Machine C. Machine B doesn't take any RO snapshots f=
or
> > > > > sending. All a receiver does is create an RW snapshot of its pare=
nt
> > > > > snapshot, apply the send stream and turn it into RO mode at the e=
nd. Even
> > > > > if all paths of some inodes are deleted in applying the send stre=
am, these
> > > > > inodes would not be deleted and become orphans after changing the=
 subvolume
> > > > > from RW to RO. Moreover, orphan inodes can occur not only in send=
 snapshots
> > > > > but also in parent snapshots because Machine B may do a batch rep=
lication
> > > > > of a couple of snapshots.
> > > > >
> > > > > An illustration for cascading backups:
> > > > > Machine A (snapshot {1..n}) --> Machine B --> Machine C
> > > > >
> > > > > The intuition to solve the problem is to delete all the items of =
orphan
> > > > > inodes before using these snapshots for sending. I used to think =
that the
> > > > > reasonable timing for doing that is during the ioctl of changing =
the
> > > > > subvolume from RW to RO because it sounds good that we will not m=
odify the
> > > > > fs tree of a RO snapshot anymore. However, attempting to do the o=
rphan
> > > > > cleanup in the ioctl would be pointless. Because if someone is ho=
lding an
> > > > > open file descriptor on the inode, the reference count of the ino=
de will
> > > > > never drop to 0. Then iput() cannot trigger eviction, which final=
ly deletes
> > > > > all the items of it. So we try to extend the original patch to ha=
ndle
> > > > > orphans in send/parent snapshots. Here are several cases that nee=
d to be
> > > > > considered:
> > > > >
> > > > > Case 1: BTRFS_COMPARE_TREE_NEW
> > > > >        |  send snapshot  | action
> > > > >  --------------------------------
> > > > >  nlink |        0        | ignore
> > > > >
> > > > > In case 1, when we get a BTRFS_COMPARE_TREE_NEW tree comparison r=
esult,
> > > > > it means that a new inode is found in the send snapshot and it do=
esn't
> > > > > appear in the parent snapshot. Since this inode has a link count =
of zero
> > > > > (It's an orphan and there're no paths for it.), we can leverage
> > > > > sctx->ignore_cur_inode in the original patch to prevent it from b=
eing
> > > > > created.
> > > > >
> > > > > Case 2: BTRFS_COMPARE_TREE_DELETED
> > > > >        | parent snapshot | action
> > > > >  ----------------------------------
> > > > >  nlink |        0        | as usual
> > > > >
> > > > > In case 2, when we get a BTRFS_COMPARE_TREE_DELETED tree comparis=
on
> > > > > result, it means that the inode only appears in the parent snapsh=
ot.
> > > > > As usual, the send operation will try to delete all its paths. Ho=
wever,
> > > > > this inode has a link count of zero, so no paths of it will be fo=
und. No
> > > > > deletion operations will be issued. We don't need to change any l=
ogic.
> > > > >
> > > > > Case 3: BTRFS_COMPARE_TREE_CHANGED
> > > > >            |       | parent snapshot | send snapshot | action
> > > > >  ----------------------------------------------------------------=
-------
> > > > >  subcase 1 | nlink |        0        |       0       | ignore
> > > > >  subcase 2 | nlink |       >0        |       0       | new_gen(de=
letion)
> > > > >  subcase 3 | nlink |        0        |      >0       | new_gen(cr=
eation)
> > > > >
> > > > > In case 3, when we get a BTRFS_COMPARE_TREE_CHANGED tree comparis=
on result,
> > > > > it means that the inode appears in both snapshots. Here're three =
subcases.
> > > > >
> > > > > First, if the inode has link counts of zero in both snapshots. Si=
nce there
> > > > > are no paths for this inode in (source/destination) parent snapsh=
ots and we
> > > > > don't care about whether there is also an orphan inode in destina=
tion or
> > > > > not, we can set sctx->ignore_cur_inode on to prevent it from bein=
g created.
> > > > >
> > > > > For the second and the third subcases, if there're paths in one s=
napshot
> > > > > and there're no paths in the other snapshot for this inode. We ca=
n treat
> > > > > this inode as a new generation. We can also leverage the logic ha=
ndling a
> > > > > new generation of an inode with small adjustments. Then it will d=
elete all
> > > > > old paths and create a new inode with new attributes and paths on=
ly when
> > > > > there's a positive link count in the send snapshot. In subcase 2,=
 the
> > > > > send operation only needs to delete all old paths as in the paren=
t
> > > > > snapshot. But it may require more operations for a directory to r=
emove its
> > > > > old paths. If a not-empty directory is going to be deleted (becau=
se it has
> > > > > a link count of zero in the send snapshot) but there're files/dir=
ectories
> > > > > with bigger inode numbers under it, the send operation will need =
to rename
> > > > > it to its orphan name first. After processing and deleting the la=
st item
> > > > > under this directory, the send operation will check this director=
y, aka
> > > > > the parent directory of the last item, again and issue a rmdir op=
eration
> > > > > to remove it finally. Therefore, we also need to treat inodes wit=
h a link
> > > > > count of zero as if they didn't exist in get_cur_inode_state(), w=
hich is
> > > > > used in process_recorded_refs(). By doing this, when reviewing a =
directory
> > > > > with orphan names after the last item under it has been deleted, =
the send
> > > > > operation now can properly issue a rmdir operation. Otherwise, wi=
thout
> > > > > doing this, the orphan directory with an orphan name would be kep=
t here
> > > > > at the end due to the existing inode with a link count of zero be=
ing found.
> > > > > In subcase 3, as in case 2, no old paths would be found, so no de=
letion
> > > > > operations will be issued. The send operation will only create a =
new one
> > > > > for that inode.
> > > > >
> > > > > Note that subcase 3 is not a common case. That's because it's eas=
y to
> > > > > reduce the hard links of an inode, but once all valid paths are r=
emoved,
> > > > > there're no valid paths for creating other hard links. The only w=
ay to do
> > > > > that is trying to send an older snapshot after a newer snapshot h=
as been
> > > > > sent.
> > > > >
> > > > > Cc: <stable@vger.kernel.org> # 4.9: 46b2f4590aab: Btrfs: fix send
> > > > > failure when root has deleted files still open
> > > > > Cc: <stable@vger.kernel.org> # 4.9: 71ecfc133b03: btrfs: send:
> > > > > introduce recorded_ref_alloc and recorded_ref_free
> > > > > Cc: <stable@vger.kernel.org> # 4.9: 3aa5bd367fa5: btrfs: send: fi=
x
> > > > > sending link commands for existing file paths
> > > > > Cc: <stable@vger.kernel.org> # 4.9: 0d8869fb6b6f8: btrfs: send: a=
lways
> > > > > use the rbtree based inode ref management infrastructure
> > > >
> > > > Btw, lines with CC, Fixes, etc, tags should not be broken even if t=
hey
> > > > are wider than 74 characters.
> > > >
> > >
> > > Okay, thank you for telling me that.
> > >
> > > > So, in v1 when I gave you that example of CC stable tags, it wasn't
> > > > meant for you to literally copy-paste them.
> > > >
> > > > First I asked if the purpose of the original Fixes tag was to backp=
ort
> > > > the fix to stable releases.
> > > > Was that the intention? You didn't provide an answer about that.
> > > >
> > >
> > > Oh, I misunderstood your suggestion. I'm sorry about that.
> > > Our intention is to report this bug and try to provide a reasonable a=
nd
> > > acceptable fix for it. Backporting is not our goal.
> > >
> > > > Then I told if that was the case, the proper way would be adding CC
> > > > stable tags and listing any
> > > > dependencies. I gave those 4 as examples with commits that are fair=
ly
> > > > recent and obvious dependencies,
> > > > but I also said that probably there's a lot more missing - especial=
ly
> > > > if we want to backport to as far as 4.9.
> > > >
> > >
> > > > Even with just those 4 dependencies, some of those commits are fair=
ly
> > > > large, and that may be frowned upon
> > > > according to stable backport rules (listed at
> > > > https://www.kernel.org/doc/Documentation/process/stable-kernel-rule=
s.rst).
> > > > For e.g., patches with over 100 lines changed.
> > > >
> > > > Now, did you actually verify if there were more dependencies? (and =
test)
> > > > And do you really want to go as far as 4.9 (currently the oldest
> > > > stable release)?
> > >
> > > No, I didn't. I used to think the CC tag was a very cool feature, whi=
ch
> > > just putting a few commits lets backport easily when I read your mail=
,
> > > so I copied and pasted these 4 commits in the beginning of revising
> > > the patch v2. However, I'm wrong.
> > >
> > > > I seriously doubt that those 4 commits are the only dependencies in
> > > > order to be able to cleanly backport to 4.9 and other old branches.
> > > >
> > > > It may be better to backport only to a few younger stable branches,=
 or
> > > > just provide later a version of the patch to
> > > > apply to each desired stable branch (once the fix is in Linus' tree
> > > > and in a -rc release).
> > > >
> > > > If you are not interested in backporting to stable or don't have th=
e
> > > > time to verify the dependencies and test, then just remove all the
> > > > stable tags.
> > > > Just leave a fixes tag:
> > > >
> > > > Fixes: 31db9f7c23fbf7 ("Btrfs: introduce BTRFS_IOC_SEND for btrfs s=
end/receive")
> > > >
> > >
> > > Since backporting is not our goal. I will just leave the fix tag here=
.
> > >
> > > > Also, please don't forget to send a test case for fstests, covering=
 as
> > > > many cases as possible (not just the example
> > > > at the beginning of the changelog).
> > > >
> > >
> > > Okay, I will submit a test case covering all cases.
> > > Because I still need to spend time learning how to use the fssum util=
ity
> > > for the last test case you reviewed, so I will submit the test case l=
ater.
> >
> > BingJing, any progress with the test case?
> > We would love to have that in fstests to help prevent regressions in th=
e future.
> >
> > Thanks.
> >
>
> Hi Filipe,
>
> I used to wait the git pull of my patch to the master branch, then I can
> attach the commit uuid in tests as before. However, it seems that there'r=
e
> troubles for the maintainer to pull all of the bug fixes into the new
> kernel 6.0 at once.

Ah, yes, it will only be in 6.1, so it should land in Linus' tree in
about 2 weeks maybe (we are at 6.0-rc6, next week is likely the final
rc7).
If you want to wait for that, it's fine. Just wanted to check if you
needed any help and that it wasn't forgotten.

Thanks!

>
> Okay, I will try to create a test covering the cases this weekend.
> Sorry for the inconvenience made.
>
> Thanks.
>
> > >
> > > Thanks.
> > >
> > > > Thanks.
> > > >
> > > > > Reviewed-by: Robbie Ko <robbieko@synology.com>
> > > > > Signed-off-by: BingJing Chang <bingjingc@synology.com>
> > > > > ---
> > > > >  fs/btrfs/send.c | 214 +++++++++++++++++++-----------------------=
------
> > > > >  1 file changed, 85 insertions(+), 129 deletions(-)
> > > > >
> > > > > diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> > > > > index f8d77a33b9b7..6ab1ba66ff4b 100644
> > > > > --- a/fs/btrfs/send.c
> > > > > +++ b/fs/btrfs/send.c
> > > > > @@ -850,6 +850,7 @@ struct btrfs_inode_info {
> > > > >         u64 gid;
> > > > >         u64 rdev;
> > > > >         u64 attr;
> > > > > +       u64 nlink;
> > > > >  };
> > > > >
> > > > >  /*
> > > > > @@ -888,6 +889,7 @@ static int get_inode_info(struct btrfs_root *=
root, u64 ino,
> > > > >         info->uid =3D btrfs_inode_uid(path->nodes[0], ii);
> > > > >         info->gid =3D btrfs_inode_gid(path->nodes[0], ii);
> > > > >         info->rdev =3D btrfs_inode_rdev(path->nodes[0], ii);
> > > > > +       info->nlink =3D btrfs_inode_nlink(path->nodes[0], ii);
> > > > >         /*
> > > > >          * Transfer the unchanged u64 value of btrfs_inode_item::=
flags, that's
> > > > >          * otherwise logically split to 32/32 parts.
> > > > > @@ -1652,19 +1654,22 @@ static int get_cur_inode_state(struct sen=
d_ctx *sctx, u64 ino, u64 gen)
> > > > >         int right_ret;
> > > > >         u64 left_gen;
> > > > >         u64 right_gen;
> > > > > +       struct btrfs_inode_info info;
> > > > >
> > > > > -       ret =3D get_inode_gen(sctx->send_root, ino, &left_gen);
> > > > > +       ret =3D get_inode_info(sctx->send_root, ino, &info);
> > > > >         if (ret < 0 && ret !=3D -ENOENT)
> > > > >                 goto out;
> > > > > -       left_ret =3D ret;
> > > > > +       left_ret =3D (info.nlink =3D=3D 0) ? -ENOENT : ret;
> > > > > +       left_gen =3D info.gen;
> > > > >
> > > > >         if (!sctx->parent_root) {
> > > > >                 right_ret =3D -ENOENT;
> > > > >         } else {
> > > > > -               ret =3D get_inode_gen(sctx->parent_root, ino, &ri=
ght_gen);
> > > > > +               ret =3D get_inode_info(sctx->parent_root, ino, &i=
nfo);
> > > > >                 if (ret < 0 && ret !=3D -ENOENT)
> > > > >                         goto out;
> > > > > -               right_ret =3D ret;
> > > > > +               right_ret =3D (info.nlink =3D=3D 0) ? -ENOENT : r=
et;
> > > > > +               right_gen =3D info.gen;
> > > > >         }
> > > > >
> > > > >         if (!left_ret && !right_ret) {
> > > > > @@ -6413,86 +6418,6 @@ static int finish_inode_if_needed(struct s=
end_ctx *sctx, int at_end)
> > > > >         return ret;
> > > > >  }
> > > > >
> > > > > -struct parent_paths_ctx {
> > > > > -       struct list_head *refs;
> > > > > -       struct send_ctx *sctx;
> > > > > -};
> > > > > -
> > > > > -static int record_parent_ref(int num, u64 dir, int index, struct=
 fs_path *name,
> > > > > -                            void *ctx)
> > > > > -{
> > > > > -       struct parent_paths_ctx *ppctx =3D ctx;
> > > > > -
> > > > > -       /*
> > > > > -        * Pass 0 as the generation for the directory, we don't c=
are about it
> > > > > -        * here as we have no new references to add, we just want=
 to delete all
> > > > > -        * references for an inode.
> > > > > -        */
> > > > > -       return record_ref_in_tree(&ppctx->sctx->rbtree_deleted_re=
fs, ppctx->refs,
> > > > > -                                 name, dir, 0, ppctx->sctx);
> > > > > -}
> > > > > -
> > > > > -/*
> > > > > - * Issue unlink operations for all paths of the current inode fo=
und in the
> > > > > - * parent snapshot.
> > > > > - */
> > > > > -static int btrfs_unlink_all_paths(struct send_ctx *sctx)
> > > > > -{
> > > > > -       LIST_HEAD(deleted_refs);
> > > > > -       struct btrfs_path *path;
> > > > > -       struct btrfs_root *root =3D sctx->parent_root;
> > > > > -       struct btrfs_key key;
> > > > > -       struct btrfs_key found_key;
> > > > > -       struct parent_paths_ctx ctx;
> > > > > -       int iter_ret =3D 0;
> > > > > -       int ret;
> > > > > -
> > > > > -       path =3D alloc_path_for_send();
> > > > > -       if (!path)
> > > > > -               return -ENOMEM;
> > > > > -
> > > > > -       key.objectid =3D sctx->cur_ino;
> > > > > -       key.type =3D BTRFS_INODE_REF_KEY;
> > > > > -       key.offset =3D 0;
> > > > > -
> > > > > -       ctx.refs =3D &deleted_refs;
> > > > > -       ctx.sctx =3D sctx;
> > > > > -
> > > > > -       btrfs_for_each_slot(root, &key, &found_key, path, iter_re=
t) {
> > > > > -               if (found_key.objectid !=3D key.objectid)
> > > > > -                       break;
> > > > > -               if (found_key.type !=3D key.type &&
> > > > > -                   found_key.type !=3D BTRFS_INODE_EXTREF_KEY)
> > > > > -                       break;
> > > > > -
> > > > > -               ret =3D iterate_inode_ref(root, path, &found_key,=
 1,
> > > > > -                                       record_parent_ref, &ctx);
> > > > > -               if (ret < 0)
> > > > > -                       goto out;
> > > > > -       }
> > > > > -       /* Catch error found during iteration */
> > > > > -       if (iter_ret < 0) {
> > > > > -               ret =3D iter_ret;
> > > > > -               goto out;
> > > > > -       }
> > > > > -
> > > > > -       while (!list_empty(&deleted_refs)) {
> > > > > -               struct recorded_ref *ref;
> > > > > -
> > > > > -               ref =3D list_first_entry(&deleted_refs, struct re=
corded_ref, list);
> > > > > -               ret =3D send_unlink(sctx, ref->full_path);
> > > > > -               if (ret < 0)
> > > > > -                       goto out;
> > > > > -               recorded_ref_free(ref);
> > > > > -       }
> > > > > -       ret =3D 0;
> > > > > -out:
> > > > > -       btrfs_free_path(path);
> > > > > -       if (ret)
> > > > > -               __free_recorded_refs(&deleted_refs);
> > > > > -       return ret;
> > > > > -}
> > > > > -
> > > > >  static void close_current_inode(struct send_ctx *sctx)
> > > > >  {
> > > > >         u64 i_size;
> > > > > @@ -6583,25 +6508,37 @@ static int changed_inode(struct send_ctx =
*sctx,
> > > > >          * file descriptor against it or turning a RO snapshot in=
to RW mode,
> > > > >          * keep an open file descriptor against a file, delete it=
 and then
> > > > >          * turn the snapshot back to RO mode before using it for =
a send
> > > > > -        * operation. So if we find such cases, ignore the inode =
and all its
> > > > > -        * items completely if it's a new inode, or if it's a cha=
nged inode
> > > > > -        * make sure all its previous paths (from the parent snap=
shot) are all
> > > > > -        * unlinked and all other the inode items are ignored.
> > > > > +        * operation. The former is what the receiver operation d=
oes.
> > > > > +        * Therefore, if we want to send these snapshots soon aft=
er they're
> > > > > +        * received, we need to handle orphan inodes as well. Mor=
eover,
> > > > > +        * orphans can appear not only in the send snapshot but a=
lso in the
> > > > > +        * parent snapshot. Here are several cases:
> > > > > +        *
> > > > > +        * Case 1: BTRFS_COMPARE_TREE_NEW
> > > > > +        *       |  send snapshot  | action
> > > > > +        * --------------------------------
> > > > > +        * nlink |        0        | ignore
> > > > > +        *
> > > > > +        * Case 2: BTRFS_COMPARE_TREE_DELETED
> > > > > +        *       | parent snapshot | action
> > > > > +        * ----------------------------------
> > > > > +        * nlink |        0        | as usual
> > > > > +        * Note: No unlinks will be sent because there're no path=
s for it.
> > > > > +        *
> > > > > +        * Case 3: BTRFS_COMPARE_TREE_CHANGED
> > > > > +        *           |       | parent snapshot | send snapshot | =
action
> > > > > +        * ------------------------------------------------------=
-----------------
> > > > > +        * subcase 1 | nlink |        0        |       0       | =
ignore
> > > > > +        * subcase 2 | nlink |       >0        |       0       | =
new_gen(deletion)
> > > > > +        * subcase 3 | nlink |        0        |      >0       | =
new_gen(creation)
> > > > > +        *
> > > > >          */
> > > > > -       if (result =3D=3D BTRFS_COMPARE_TREE_NEW ||
> > > > > -           result =3D=3D BTRFS_COMPARE_TREE_CHANGED) {
> > > > > -               u32 nlinks;
> > > > > -
> > > > > -               nlinks =3D btrfs_inode_nlink(sctx->left_path->nod=
es[0], left_ii);
> > > > > -               if (nlinks =3D=3D 0) {
> > > > > +       if (result =3D=3D BTRFS_COMPARE_TREE_NEW) {
> > > > > +               if (btrfs_inode_nlink(sctx->left_path->nodes[0], =
left_ii) =3D=3D
> > > > > +                                     0) {
> > > > >                         sctx->ignore_cur_inode =3D true;
> > > > > -                       if (result =3D=3D BTRFS_COMPARE_TREE_CHAN=
GED)
> > > > > -                               ret =3D btrfs_unlink_all_paths(sc=
tx);
> > > > >                         goto out;
> > > > >                 }
> > > > > -       }
> > > > > -
> > > > > -       if (result =3D=3D BTRFS_COMPARE_TREE_NEW) {
> > > > >                 sctx->cur_inode_gen =3D left_gen;
> > > > >                 sctx->cur_inode_new =3D true;
> > > > >                 sctx->cur_inode_deleted =3D false;
> > > > > @@ -6622,6 +6559,18 @@ static int changed_inode(struct send_ctx *=
sctx,
> > > > >                 sctx->cur_inode_mode =3D btrfs_inode_mode(
> > > > >                                 sctx->right_path->nodes[0], right=
_ii);
> > > > >         } else if (result =3D=3D BTRFS_COMPARE_TREE_CHANGED) {
> > > > > +               u32 new_nlinks, old_nlinks;
> > > > > +
> > > > > +               new_nlinks =3D btrfs_inode_nlink(sctx->left_path-=
>nodes[0],
> > > > > +                                              left_ii);
> > > > > +               old_nlinks =3D btrfs_inode_nlink(sctx->right_path=
->nodes[0],
> > > > > +                                              right_ii);
> > > > > +               if (new_nlinks =3D=3D 0 && old_nlinks =3D=3D 0) {
> > > > > +                       sctx->ignore_cur_inode =3D true;
> > > > > +                       goto out;
> > > > > +               } else if (new_nlinks =3D=3D 0 || old_nlinks =3D=
=3D 0) {
> > > > > +                       sctx->cur_inode_new_gen =3D 1;
> > > > > +               }
> > > > >                 /*
> > > > >                  * We need to do some special handling in case th=
e inode was
> > > > >                  * reported as changed with a changed generation =
number. This
> > > > > @@ -6648,38 +6597,45 @@ static int changed_inode(struct send_ctx =
*sctx,
> > > > >                         /*
> > > > >                          * Now process the inode as if it was new=
.
> > > > >                          */
> > > > > -                       sctx->cur_inode_gen =3D left_gen;
> > > > > -                       sctx->cur_inode_new =3D true;
> > > > > -                       sctx->cur_inode_deleted =3D false;
> > > > > -                       sctx->cur_inode_size =3D btrfs_inode_size=
(
> > > > > -                                       sctx->left_path->nodes[0]=
, left_ii);
> > > > > -                       sctx->cur_inode_mode =3D btrfs_inode_mode=
(
> > > > > -                                       sctx->left_path->nodes[0]=
, left_ii);
> > > > > -                       sctx->cur_inode_rdev =3D btrfs_inode_rdev=
(
> > > > > -                                       sctx->left_path->nodes[0]=
, left_ii);
> > > > > -                       ret =3D send_create_inode_if_needed(sctx)=
;
> > > > > -                       if (ret < 0)
> > > > > -                               goto out;
> > > > > +                       if (new_nlinks > 0) {
> > > > > +                               sctx->cur_inode_gen =3D left_gen;
> > > > > +                               sctx->cur_inode_new =3D true;
> > > > > +                               sctx->cur_inode_deleted =3D false=
;
> > > > > +                               sctx->cur_inode_size =3D btrfs_in=
ode_size(
> > > > > +                                               sctx->left_path->=
nodes[0],
> > > > > +                                               left_ii);
> > > > > +                               sctx->cur_inode_mode =3D btrfs_in=
ode_mode(
> > > > > +                                               sctx->left_path->=
nodes[0],
> > > > > +                                               left_ii);
> > > > > +                               sctx->cur_inode_rdev =3D btrfs_in=
ode_rdev(
> > > > > +                                               sctx->left_path->=
nodes[0],
> > > > > +                                               left_ii);
> > > > > +                               ret =3D send_create_inode_if_need=
ed(sctx);
> > > > > +                               if (ret < 0)
> > > > > +                                       goto out;
> > > > >
> > > > > -                       ret =3D process_all_refs(sctx, BTRFS_COMP=
ARE_TREE_NEW);
> > > > > -                       if (ret < 0)
> > > > > -                               goto out;
> > > > > -                       /*
> > > > > -                        * Advance send_progress now as we did no=
t get into
> > > > > -                        * process_recorded_refs_if_needed in the=
 new_gen case.
> > > > > -                        */
> > > > > -                       sctx->send_progress =3D sctx->cur_ino + 1=
;
> > > > > +                               ret =3D process_all_refs(sctx,
> > > > > +                                               BTRFS_COMPARE_TRE=
E_NEW);
> > > > > +                               if (ret < 0)
> > > > > +                                       goto out;
> > > > > +                               /*
> > > > > +                                * Advance send_progress now as w=
e did not get
> > > > > +                                * into process_recorded_refs_if_=
needed in the
> > > > > +                                * new_gen case.
> > > > > +                                */
> > > > > +                               sctx->send_progress =3D sctx->cur=
_ino + 1;
> > > > >
> > > > > -                       /*
> > > > > -                        * Now process all extents and xattrs of =
the inode as if
> > > > > -                        * they were all new.
> > > > > -                        */
> > > > > -                       ret =3D process_all_extents(sctx);
> > > > > -                       if (ret < 0)
> > > > > -                               goto out;
> > > > > -                       ret =3D process_all_new_xattrs(sctx);
> > > > > -                       if (ret < 0)
> > > > > -                               goto out;
> > > > > +                               /*
> > > > > +                                * Now process all extents and xa=
ttrs of the
> > > > > +                                * inode as if they were all new.
> > > > > +                                */
> > > > > +                               ret =3D process_all_extents(sctx)=
;
> > > > > +                               if (ret < 0)
> > > > > +                                       goto out;
> > > > > +                               ret =3D process_all_new_xattrs(sc=
tx);
> > > > > +                               if (ret < 0)
> > > > > +                                       goto out;
> > > > > +                       }
> > > > >                 } else {
> > > > >                         sctx->cur_inode_gen =3D left_gen;
> > > > >                         sctx->cur_inode_new =3D false;
> > > > > --
> > > > > 2.37.1
> > > > >