From 0c628c3152a727fff287a98897d83ee45ad990e5 Mon Sep 17 00:00:00 2001 From: Dean Deng Date: Tue, 23 Jun 2020 16:11:31 -0700 Subject: Support inotify in vfs2 gofer fs. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Because there is no inode structure stored in the sandbox, inotify watches must be held on the dentry. This would be an issue in the presence of hard links, where multiple dentries would need to share the same set of watches, but in VFS2, we do not support the internal creation of hard links on gofer fs. As a result, we make the assumption that every dentry corresponds to a unique inode. Furthermore, dentries can be cached and then evicted, even if the underlying file has not be deleted. We must prevent this from occurring if there are any watches that would be lost. Note that if the dentry was deleted or invalidated (d.vfsd.IsDead()), we should still destroy it along with its watches. Additionally, when a dentry’s last watch is removed, we cache it if it also has zero references. This way, the dentry can eventually be evicted from memory if it is no longer needed. This is accomplished with a new dentry method, OnZeroWatches(), which is called by Inotify.RmWatch and Inotify.Release. Note that it must be called after all inotify locks are released to avoid violating lock order. Stress tests are added to make sure that inotify operations don't deadlock with gofer.OnZeroWatches. Updates #1479. PiperOrigin-RevId: 317958034 --- pkg/sentry/syscalls/linux/vfs2/inotify.go | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'pkg/sentry/syscalls/linux/vfs2') diff --git a/pkg/sentry/syscalls/linux/vfs2/inotify.go b/pkg/sentry/syscalls/linux/vfs2/inotify.go index 7d50b6a16..74e5287b7 100644 --- a/pkg/sentry/syscalls/linux/vfs2/inotify.go +++ b/pkg/sentry/syscalls/linux/vfs2/inotify.go @@ -116,8 +116,11 @@ func InotifyAddWatch(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kern } defer d.DecRef() - fd = ino.AddWatch(d.Dentry(), mask) - return uintptr(fd), nil, err + fd, err = ino.AddWatch(d.Dentry(), mask) + if err != nil { + return 0, nil, err + } + return uintptr(fd), nil, nil } // InotifyRmWatch implements the inotify_rm_watch() syscall. -- cgit v1.2.3