When revalidating a Dirent, if the inode id is the same, then we don't need to
throw away the entire Dirent. We can just update the unstable attributes in
place.
If the inode id has changed, then the remote file has been deleted or moved,
and we have no choice but to throw away the dirent we have a look up another.
In this case, we may still end up losing a mounted dirent that is a child of
the revalidated dirent. However, that seems appropriate here because the entire
mount point has been pulled out from underneath us.
Because gVisor's overlay is at the Inode level rather than the Dirent level, we
must pass the parent Inode and name along with the Inode that is being
revalidated.
PiperOrigin-RevId: 210431270
Change-Id: I705caef9c68900234972d5aac4ae3a78c61c7d42
Previously, gofer filesystems were configured with the default "fscache"
policy, which caches filesystem metadata and contents aggressively. While this
setting is best for performance, it means that changes from inside the sandbox
may not be immediately propagated outside the sandbox, and vice-versa.
This CL changes volumes and the root fs configuration to use a new
"remote-revalidate" cache policy which tries to retain as much caching as
possible while still making fs changes visible across the sandbox boundary.
This cache policy is enabled by default for the root filesystem. The default
value for the "--file-access" flag is still "proxy", but the behavior is
changed to use the new cache policy.
A new value for the "--file-access" flag is added, called "proxy-exclusive",
which turns on the previous aggressive caching behavior. As the name implies,
this flag should be used when the sandbox has "exclusive" access to the
filesystem.
All volume mounts are configured to use the new cache policy, since it is
safest and most likely to be correct. There is not currently a way to change
this behavior, but it's possible to add such a mechanism in the future. The
configurability is a smaller issue for volumes, since most of the expensive
application fs operations (walking + stating files) will likely served by the
root fs.
PiperOrigin-RevId: 208735037
Change-Id: Ife048fab1948205f6665df8563434dbc6ca8cfc9
This CL adds a new cache-policy for gofer filesystems that uses the host page
cache, but causes dirents to be reloaded on each Walk, and does not cache
readdir results.
This policy is useful when the remote filesystem may change out from underneath
us, as any remote changes will be reflected on the next Walk.
Importantly, this cache policy is only consistent if we do not use gVisor's
internal page cache, since that page cache is tied to the Inode and may be
thrown away upon Revalidation.
This cache policy should only be used when the gofer supports donating host
FDs, since then gVisor will make use of the host kernel page cache, which will
be consistent for all open files in the gofer. In fact, a panic will be raised
if a file is opened without a donated FD.
PiperOrigin-RevId: 207752937
Change-Id: I233cb78b4695bbe00a4605ae64080a47629329b8
The new policy is identical to FSCACHE (which caches everything in memory), but
it also flushes writes to the backing fs agent immediately.
All gofer cache policy decisions have been moved into the cachePolicy type.
Previously they were sprinkled around the codebase.
There are many different things that we cache (page cache, negative dirents,
dirent LRU, unstable attrs, readdir results....), and I don't think we should
have individual flags to control each of these. Instead, we should have a few
high-level cache policies that are consistent and useful to users. This
refactoring makes it easy to add more such policies.
PiperOrigin-RevId: 201206937
Change-Id: I6e225c382b2e5e1b0ad4ccf8ca229873f4cd389d
Nicolas Lacasse