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- Check write permission on truncate(2). Unlike ftruncate(2),
truncate(2) fails if the user does not have write permissions
on the file.
- For gofers under InteropModeShared, check file type before
making a truncate request. We should fail early and avoid
making an rpc when possible. Furthermore, depending on the
remote host's failure may give us unexpected behavior--if the
host converts the truncate request to an ftruncate syscall on
an open fd, we will get EINVAL instead of EISDIR.
Updates #2923.
PiperOrigin-RevId: 322913569
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Fix typos.
PiperOrigin-RevId: 322913282
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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
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Updates #1035, #1199
PiperOrigin-RevId: 317028108
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- Change FileDescriptionImpl Lock/UnlockPOSIX signature to
take {start,length,whence}, so the correct offset can be
calculated in the implementations.
- Create PosixLocker interface to make it possible to share
the same locking code from different implementations.
Closes #1480
PiperOrigin-RevId: 316910286
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Major differences from existing overlay filesystems:
- Linux allows lower layers in an overlay to require revalidation, but not the
upper layer. VFS1 allows the upper layer in an overlay to require
revalidation, but not the lower layer. VFS2 does not allow any layers to
require revalidation. (Now that vfs.MkdirOptions.ForSyntheticMountpoint
exists, no uses of overlay in VFS1 are believed to require upper layer
revalidation; in particular, the requirement that the upper layer support the
creation of "trusted." extended attributes for whiteouts effectively required
the upper filesystem to be tmpfs in most cases.)
- Like VFS1, but unlike Linux, VFS2 overlay does not attempt to make mutations
of the upper layer atomic using a working directory and features like
RENAME_WHITEOUT. (This may change in the future, since not having a working
directory makes error recovery for some operations, e.g. rmdir, particularly
painful.)
- Like Linux, but unlike VFS1, VFS2 represents whiteouts using character
devices with rdev == 0; the equivalent of the whiteout attribute on
directories is xattr trusted.overlay.opaque = "y"; and there is no equivalent
to the whiteout attribute on non-directories since non-directories are never
merged with lower layers.
- Device and inode numbers work as follows:
- In Linux, modulo the xino feature and a special case for when all layers
are the same filesystem:
- Directories use the overlay filesystem's device number and an
ephemeral inode number assigned by the overlay.
- Non-directories that have been copied up use the device and inode
number assigned by the upper filesystem.
- Non-directories that have not been copied up use a per-(overlay,
layer)-pair device number and the inode number assigned by the lower
filesystem.
- In VFS1, device and inode numbers always come from the lower layer unless
"whited out"; this has the adverse effect of requiring interaction with
the lower filesystem even for non-directory files that exist on the upper
layer.
- In VFS2, device and inode numbers are assigned as in Linux, except that
xino and the samefs special case are not supported.
- Like Linux, but unlike VFS1, VFS2 does not attempt to maintain memory mapping
coherence across copy-up. (This may have to change in the future, as users
may be dependent on this property.)
- Like Linux, but unlike VFS1, VFS2 uses the overlayfs mounter's credentials
when interacting with the overlay's layers, rather than the caller's.
- Like Linux, but unlike VFS1, VFS2 permits multiple lower layers in an
overlay.
- Like Linux, but unlike VFS1, VFS2's overlay filesystem is
application-mountable.
Updates #1199
PiperOrigin-RevId: 316019067
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