[cephfs] snapshot names are too long

[Goutham Pacha Ravi]

Description
===========
This issue was first reported on the CephFS mailing list: https://<email address hidden>/thread/VREULFBGVN43TN4L3CR6LFXWN3NGJ7K3/
Relevant excerpt from that post:

```````````

The Manila driver creates pretty long subvolume snapshot names:
https://github.com/openstack/manila/blob/master/manila/share/drivers/cephfs…
Ex: 3c42f809-4b10-4877-911d-c68910747ae5_eb90c527-9de4-4f57-87bf-6b06f57a396c

And we have trouble accessing those.

It works with a recent kernel this way:

# ls
/cephfs-pam-fuse/volumes/_nogroup/dbebbb35-31f1-47e5-ac75-48d65a1ee33c/.snap/3c42f809-4b10-4877-911d-c68910747ae5_eb90c527-9de4-4f57-87bf-6b06f57a396c/fe1b97f3-3481-43a9-a677-c9424544de09/
now
#

But we cannot see the "now" file when listing via .snap in a subdir:

# ls
/cephfs-pam-fuse/volumes/_nogroup/dbebbb35-31f1-47e5-ac75-48d65a1ee33c/fe1b97f3-3481-43a9-a677-c9424544de09/.snap/_3c42f809-4b10-4877-911d-c68910747ae5_eb90c527-9de4-4f57-87bf-6b06f57a396c_1100/
#

(Subvolume_V2 users always mount the subdir, so they can only ever
access snaps via the subdir path, btw).

The kernel client has the same issue (confirmed with latest CentOS
Stream 8 kernel).

And btw old kernels can't even list this dir. Here is the latest
CentOS 7 kernel:

# ls
/cephfs-pam/volumes/_nogroup/dbebbb35-31f1-47e5-ac75-48d65a1ee33c/fe1b97f3-3481-43a9-a677-c9424544de09/.snap/
ls: cannot access
/cephfs-pam/volumes/_nogroup/dbebbb35-31f1-47e5-ac75-48d65a1ee33c/fe1b97f3-3481-43a9-a677-c9424544de09/.snap/_3c42f809-4b10-4877-911d-c68910747ae5_eb90c527-9de4-4f57-87bf-6b06f57a396c_1100:
No such file or directory
_3c42f809-4b10-4877-911d-c68910747ae5_eb90c527-9de4-4f57-87bf-6b06f57a396c_1100

I think this is all because the snap name is too long.
Notice that the subdir snap has _1100 appended -- this is supposed to
be the inode of the place where the snap was taken (IIUC) -- but it
has been truncated to 80 chars, presumably because of
https://github.com/ceph/ceph/blob/master/src/mds/snap.cc#L87

``````````````

Steps to reproduce
==================

* Setup the CephFS driver (doesn't matter if using Native/NFS)
* Create a share and a snapshot
* Mount the share and navigate to the .snap directory and try walking down the snap tree for the snapshot created.

Expected result
===============
Directory walk is permitted into the read only snapshot directories

Actual result
=============
Directory walk isn't possible due to errors.

Environment
===========
1. Victoria+ releases of OpenStack Manila (manila driver started using the ceph mgr interface in this OpenStack release)

2. Which storage backend did you use?
   Ceph
   What's the version of that? Octopus

[Vida Haririan (vhariria)]

See additional discussions at https://meetings.opendev.org/meetings/manila/2022/manila.2022-04-21-15.00.log.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/manila/+/862348

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/862348
Committed: https://opendev.org/openstack/manila/commit/c86523d5909a2d61e03fb29f4c0c71b67cf18205
Submitter: "Zuul (22348)"
Branch: master

commit c86523d5909a2d61e03fb29f4c0c71b67cf18205
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/2023.2
Review: https://review.opendev.org/c/openstack/manila/+/896321

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/896321
Committed: https://opendev.org/openstack/manila/commit/4d4d4bdb118968b1cb089fa8b415c8354874e3a7
Submitter: "Zuul (22348)"
Branch: stable/2023.2

commit 4d4d4bdb118968b1cb089fa8b415c8354874e3a7
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf
    (cherry picked from commit c86523d5909a2d61e03fb29f4c0c71b67cf18205)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/2023.1
Review: https://review.opendev.org/c/openstack/manila/+/897969

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/zed
Review: https://review.opendev.org/c/openstack/manila/+/897970

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila 17.1.0 release.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/897969
Committed: https://opendev.org/openstack/manila/commit/3be5df4e1fe5feac43c3c1524eb00c4441eec476
Submitter: "Zuul (22348)"
Branch: stable/2023.1

commit 3be5df4e1fe5feac43c3c1524eb00c4441eec476
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf
    (cherry picked from commit c86523d5909a2d61e03fb29f4c0c71b67cf18205)
    (cherry picked from commit 4d4d4bdb118968b1cb089fa8b415c8354874e3a7)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/yoga
Review: https://review.opendev.org/c/openstack/manila/+/901282

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/xena
Review: https://review.opendev.org/c/openstack/manila/+/901283

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/manila/+/901284

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/897970
Committed: https://opendev.org/openstack/manila/commit/569a30df0533fe1bd0b53d5111d801353a1dc126
Submitter: "Zuul (22348)"
Branch: stable/zed

commit 569a30df0533fe1bd0b53d5111d801353a1dc126
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf
    (cherry picked from commit c86523d5909a2d61e03fb29f4c0c71b67cf18205)
    (cherry picked from commit 4d4d4bdb118968b1cb089fa8b415c8354874e3a7)
    (cherry picked from commit 3be5df4e1fe5feac43c3c1524eb00c4441eec476)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/901282
Committed: https://opendev.org/openstack/manila/commit/67187c28fae622d679362adf4c68f968ce33473e
Submitter: "Zuul (22348)"
Branch: stable/yoga

commit 67187c28fae622d679362adf4c68f968ce33473e
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf
    (cherry picked from commit c86523d5909a2d61e03fb29f4c0c71b67cf18205)
    (cherry picked from commit 4d4d4bdb118968b1cb089fa8b415c8354874e3a7)
    (cherry picked from commit 3be5df4e1fe5feac43c3c1524eb00c4441eec476)
    (cherry picked from commit 569a30df0533fe1bd0b53d5111d801353a1dc126)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/manila/+/901283
Committed: https://opendev.org/openstack/manila/commit/823e1b416910c41d45551fe345e12f321bae3ca8
Submitter: "Zuul (22348)"
Branch: stable/xena

commit 823e1b416910c41d45551fe345e12f321bae3ca8
Author: Victoria Martinez de la Cruz <email address hidden>
Date: Mon Sep 19 08:31:13 2022 +0000

    Shorten snapshots names in CephFS drivers

    The name set to snapshots in the CephFS drivers
    is generated appending the snapshot id with the
    snapshot instance id.

    This is a problem because Ceph has a limitation
    in the name of the subvolumes (shares) being created.

    What happens then is, when trying to create a snapshot,
    the snapshot gets created with a truncated name and it cannot
    be accessed later.

    This change drops the snapshot instance id from the
    assigned name in order to avoid this limitation.

    Closes-Bug: #1967760

    Change-Id: Ifab3ec9de2abeb1af8e6499feca0236e1ee22fcf
    (cherry picked from commit c86523d5909a2d61e03fb29f4c0c71b67cf18205)
    (cherry picked from commit 4d4d4bdb118968b1cb089fa8b415c8354874e3a7)
    (cherry picked from commit 3be5df4e1fe5feac43c3c1524eb00c4441eec476)
    (cherry picked from commit 569a30df0533fe1bd0b53d5111d801353a1dc126)
    (cherry picked from commit 67187c28fae622d679362adf4c68f968ce33473e)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila 16.2.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila 15.4.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila 14.2.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila xena-eom release.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/manila/+/901284
Reason: stable/wallaby branch of openstack/manila is about to be deleted. To be able to do that, all open patches need to be abandoned. Please cherry pick the patch to unmaintained/wallaby if you want to further work on this patch.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: unmaintained/wallaby
Review: https://review.opendev.org/c/openstack/manila/+/911619

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/manila 18.0.0.0rc1 release candidate.