From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Howells Date: Mon, 30 Mar 2020 14:36:54 +0000 Subject: [GIT PULL] Mount and superblock notifications Message-Id: <1449543.1585579014@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <1445647.1585576702@warthog.procyon.org.uk> To: torvalds@linux-foundation.org Cc: dhowells@redhat.com, viro@zeniv.linux.org.uk, dray@redhat.com, kzak@redhat.com, mszeredi@redhat.com, swhiteho@redhat.com, jlayton@redhat.com, raven@themaw.net, andres@anarazel.de, christian.brauner@ubuntu.com, keyrings@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Hi Linus, If you could consider pulling this - or would you prefer it to go through Al? It adds a couple of VFS-related event sources for the general notification mechanism: (1) Mount topology events, such as mounting, unmounting, mount expiry, mount reconfiguration. (2) Superblock events, such as R/W<->R/O changes, quota overrun and I/O errors (not complete yet). WHY === (1) Mount notifications. This one is wanted to avoid repeated trawling of /proc/mounts or similar to work out changes to the mount object attributes and mount topology. I'm told that the proc file holding the namespace_sem is a point of contention, especially as the process of generating the text descriptions of the mounts/superblocks can be quite involved. Whilst you can use poll() on /proc/mounts, it doesn't give you any clues as to what changed. The notification generated here directly indicates the mounts involved in any particular event and gives an idea of what the change was. This is combined with a new fsinfo() system call that allows, amongst other things, the ability to retrieve in one go an { id, change_counter } tuple from all the children of a specified mount, allowing buffer overruns to be dealt with quickly. This can be used by systemd to improve efficiency: https://lore.kernel.org/linux-fsdevel/20200227151421.3u74ijhqt6ekbiss@ws.net.home/ And it's not just Red Hat that's potentially interested in this: https://lore.kernel.org/linux-fsdevel/293c9bd3-f530-d75e-c353-ddeabac27cf6@6wind.com/ Also, this can be used to improve management of containers by allowing watches to be set in foreign mount namespaces, such as are in a container. (2) Superblock notifications. This one is provided to allow systemd or the desktop to more easily detect events such as I/O errors and EDQUOT/ENOSPC. This would be of interest to Postgres: https://lore.kernel.org/linux-fsdevel/20200211005626.7yqjf5rbs3vbwagd@alap3.anarazel.de/ But could also be used to indicate to systemd when a superblock has had its configuration changed. Thanks, David --- The following changes since commit 694435dbde3d1da79aafaf4cd680802f9eb229b7: smack: Implement the watch_key and post_notification hooks (2020-03-19 17:31:09 +0000) are available in the Git repository at: git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git tags/notifications-fs-20200330 for you to fetch changes up to 8dbf1aa122da5bbb4ede0f363a8a18dfc723be33: watch_queue: sample: Display superblock notifications (2020-03-19 17:31:09 +0000) ---------------------------------------------------------------- Filesystem notifications ---------------------------------------------------------------- David Howells (6): watch_queue: Add security hooks to rule on setting mount and sb watches watch_queue: Implement mount topology and attribute change notifications watch_queue: sample: Display mount tree change notifications watch_queue: Introduce a non-repeating system-unique superblock ID watch_queue: Add superblock notifications watch_queue: sample: Display superblock notifications Documentation/watch_queue.rst | 24 ++- arch/alpha/kernel/syscalls/syscall.tbl | 2 + arch/arm/tools/syscall.tbl | 2 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 4 + arch/ia64/kernel/syscalls/syscall.tbl | 2 + arch/m68k/kernel/syscalls/syscall.tbl | 2 + arch/microblaze/kernel/syscalls/syscall.tbl | 2 + arch/mips/kernel/syscalls/syscall_n32.tbl | 2 + arch/mips/kernel/syscalls/syscall_n64.tbl | 2 + arch/mips/kernel/syscalls/syscall_o32.tbl | 2 + arch/parisc/kernel/syscalls/syscall.tbl | 2 + arch/powerpc/kernel/syscalls/syscall.tbl | 2 + arch/s390/kernel/syscalls/syscall.tbl | 2 + arch/sh/kernel/syscalls/syscall.tbl | 2 + arch/sparc/kernel/syscalls/syscall.tbl | 2 + arch/x86/entry/syscalls/syscall_32.tbl | 2 + arch/x86/entry/syscalls/syscall_64.tbl | 2 + arch/xtensa/kernel/syscalls/syscall.tbl | 2 + fs/Kconfig | 21 +++ fs/Makefile | 1 + fs/internal.h | 1 + fs/mount.h | 21 +++ fs/mount_notify.c | 228 ++++++++++++++++++++++++++++ fs/namespace.c | 22 +++ fs/super.c | 205 +++++++++++++++++++++++++ include/linux/dcache.h | 1 + include/linux/fs.h | 62 ++++++++ include/linux/lsm_hooks.h | 24 +++ include/linux/security.h | 16 ++ include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 6 +- include/uapi/linux/watch_queue.h | 65 +++++++- kernel/sys_ni.c | 6 + samples/watch_queue/watch_test.c | 81 +++++++++- security/security.c | 14 ++ 36 files changed, 835 insertions(+), 5 deletions(-) create mode 100644 fs/mount_notify.c