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Update inotify documentation for gofer filesystem.

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We now allow hard links to be created within gofer fs (see
github.com/google/gvisor/commit/f20e63e31b56784c596897e86f03441f9d05f567).
Update the inotify documentation accordingly.

PiperOrigin-RevId: 328177485
This commit is contained in:
Dean Deng
2020-08-24 11:30:44 -07:00
committed by gVisor bot
parent 89791a79bf
commit bae25d2a08
3 changed files with 23 additions and 16 deletions
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pkg/sentry/fsimpl/gofer/gofer.go
+7
View File
@@ -703,6 +703,13 @@ type dentry struct {
locks vfs.FileLocks
// Inotify watches for this dentry.
//
// Note that inotify may behave unexpectedly in the presence of hard links,
// because dentries corresponding to the same file have separate inotify
// watches when they should share the same set. This is the case because it is
// impossible for us to know for sure whether two dentries correspond to the
// same underlying file (see the gofer filesystem section fo vfs/inotify.md for
// a more in-depth discussion on this matter).
watches vfs.Watches
}
pkg/sentry/syscalls/linux/linux64.go
+7 -7
View File
@@ -305,9 +305,9 @@ var AMD64 = &kernel.SyscallTable{
250: syscalls.Error("keyctl", syserror.EACCES, "Not available to user.", nil),
251: syscalls.CapError("ioprio_set", linux.CAP_SYS_ADMIN, "", nil), // requires cap_sys_nice or cap_sys_admin (depending)
252: syscalls.CapError("ioprio_get", linux.CAP_SYS_ADMIN, "", nil), // requires cap_sys_nice or cap_sys_admin (depending)
253: syscalls.PartiallySupported("inotify_init", InotifyInit, "inotify events are only available inside the sandbox.", nil),
254: syscalls.PartiallySupported("inotify_add_watch", InotifyAddWatch, "inotify events are only available inside the sandbox.", nil),
255: syscalls.PartiallySupported("inotify_rm_watch", InotifyRmWatch, "inotify events are only available inside the sandbox.", nil),
253: syscalls.PartiallySupported("inotify_init", InotifyInit, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
254: syscalls.PartiallySupported("inotify_add_watch", InotifyAddWatch, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
255: syscalls.PartiallySupported("inotify_rm_watch", InotifyRmWatch, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
256: syscalls.CapError("migrate_pages", linux.CAP_SYS_NICE, "", nil),
257: syscalls.Supported("openat", Openat),
258: syscalls.Supported("mkdirat", Mkdirat),
@@ -346,7 +346,7 @@ var AMD64 = &kernel.SyscallTable{
291: syscalls.Supported("epoll_create1", EpollCreate1),
292: syscalls.Supported("dup3", Dup3),
293: syscalls.Supported("pipe2", Pipe2),
294: syscalls.Supported("inotify_init1", InotifyInit1),
294: syscalls.PartiallySupported("inotify_init1", InotifyInit1, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
295: syscalls.Supported("preadv", Preadv),
296: syscalls.Supported("pwritev", Pwritev),
297: syscalls.Supported("rt_tgsigqueueinfo", RtTgsigqueueinfo),
@@ -454,9 +454,9 @@ var ARM64 = &kernel.SyscallTable{
23: syscalls.Supported("dup", Dup),
24: syscalls.Supported("dup3", Dup3),
25: syscalls.PartiallySupported("fcntl", Fcntl, "Not all options are supported.", nil),
26: syscalls.Supported("inotify_init1", InotifyInit1),
27: syscalls.PartiallySupported("inotify_add_watch", InotifyAddWatch, "inotify events are only available inside the sandbox.", nil),
28: syscalls.PartiallySupported("inotify_rm_watch", InotifyRmWatch, "inotify events are only available inside the sandbox.", nil),
26: syscalls.PartiallySupported("inotify_init1", InotifyInit1, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
27: syscalls.PartiallySupported("inotify_add_watch", InotifyAddWatch, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
28: syscalls.PartiallySupported("inotify_rm_watch", InotifyRmWatch, "Inotify events are only available inside the sandbox. Hard links are treated as different watch targets in gofer fs.", nil),
29: syscalls.PartiallySupported("ioctl", Ioctl, "Only a few ioctls are implemented for backing devices and file systems.", nil),
30: syscalls.CapError("ioprio_set", linux.CAP_SYS_ADMIN, "", nil), // requires cap_sys_nice or cap_sys_admin (depending)
31: syscalls.CapError("ioprio_get", linux.CAP_SYS_ADMIN, "", nil), // requires cap_sys_nice or cap_sys_admin (depending)
pkg/sentry/vfs/g3doc/inotify.md
+9 -9
View File
@@ -28,9 +28,9 @@ The set of all watches held on a single file (i.e., the watch target) is stored
in vfs.Watches. Each watch will belong to a different inotify instance (an
instance can only have one watch on any watch target). The watches are stored in
a map indexed by their vfs.Inotify owner’s id. Hard links and file descriptions
to a single file will all share the same vfs.Watches. Activity on the target
causes its vfs.Watches to generate notifications on its watches’ inotify
instances.
to a single file will all share the same vfs.Watches (with the exception of the
gofer filesystem, described in a later section). Activity on the target causes
its vfs.Watches to generate notifications on its watches’ inotify instances.
### vfs.Watch
@@ -103,12 +103,12 @@ inotify:
unopened p9 file (and possibly an open FID), through which the Sentry
interacts with the gofer.
* *Solution:* 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. However, the next point
raises an issue with this assumption:
inotify watches must be held on the dentry. For the purposes of inotify,
we assume that every dentry corresponds to a unique inode, which may
cause unexpected behavior in the presence of hard links, where multiple
dentries should share the same set of watches. Indeed, it is impossible
for us to be absolutely sure whether dentries correspond to the same
file or not, due to the following point:
* **The Sentry cannot always be aware of hard links on the remote
filesystem.** There is no way for us to confirm whether two files on the
remote filesystem are actually links to the same inode. QIDs and inodes are