Re: [PATCH 2/2] pidfd: add pidfdfs

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On 13. 02. 24, 17:45, Christian Brauner wrote:
This moves pidfds from the anonymous inode infrastructure to a tiny
pseudo filesystem. This has been on my todo for quite a while as it will
unblock further work that we weren't able to do simply because of the
very justified limitations of anonymous inodes. Moving pidfds to a tiny
pseudo filesystem allows:

* statx() on pidfds becomes useful for the first time.
* pidfds can be compared simply via statx() and then comparing inode
* pidfds have unique inode numbers for the system lifetime.
* struct pid is now stashed in inode->i_private instead of
   file->private_data. This means it is now possible to introduce
   concepts that operate on a process once all file descriptors have been
   closed. A concrete example is kill-on-last-close.
* file->private_data is freed up for per-file options for pidfds.
* Each struct pid will refer to a different inode but the same struct
   pid will refer to the same inode if it's opened multiple times. In
   contrast to now where each struct pid refers to the same inode. Even
   if we were to move to anon_inode_create_getfile() which creates new
   inodes we'd still be associating the same struct pid with multiple
   different inodes.
* Pidfds now go through the regular dentry_open() path which means that
   all security hooks are called unblocking proper LSM management for
   pidfds. In addition fsnotify hooks are called and allow for listening
   to open events on pidfds.

The tiny pseudo filesystem is not visible anywhere in userspace exactly
like e.g., pipefs and sockfs. There's no lookup, there's no complex
inode operations, nothing. Dentries and inodes are always deleted when
the last pidfd is closed.

This breaks lsof and util-linux.

Without the commit, lsof shows:
systemd      ... 59 [pidfd:899]

With the commit:
systemd      ... 1187 pidfd

And that user-visible change breaks a lot of stuff, incl. lsof tests.

For util-linux, its test fail with:

[  125s] --- tests/expected/lsfd/column-name-pidfd	2024-05-06 07:20:54.655845940 +0000
[  125s] +++ tests/output/lsfd/column-name-pidfd	2024-05-15 01:04:15.406666666 +0000
[  125s] @@ -1,2 +1,2 @@
[  125s] -3 anon_inode:[pidfd] pid=1 comm= nspid=1
[  125s] +3 pidfd:[INODENUM] pidfd:[INODENUM]
[  125s]  pidfd:ASSOC,KNAME,NAME: 0
[  125s]          lsfd: NAME and KNAME column: [02] pidfd             ... FAILED (lsfd/column-name-pidfd)

[  125s] --- tests/expected/lsfd/column-type-pidfd	2024-05-06 07:20:54.655845940 +0000
[  125s] +++ tests/output/lsfd/column-type-pidfd	2024-05-15 01:04:15.573333333 +0000
[  125s] @@ -1,2 +1,2 @@
[  125s] -3 UNKN pidfd
[  125s] +3 REG REG
[  125s]  pidfd:ASSOC,STTYPE,TYPE: 0
[  125s]          lsfd: TYPE and STTYPE column: [02] pidfd            ... FAILED (lsfd/column-type-pidfd)

Any ideas?

suse labs

[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [NTFS 3]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [NTFS 3]     [Samba]     [Device Mapper]     [CEPH Development]

  Powered by Linux