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