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Updates #1198
Opening host pipes (by spinning in fdpipe) and host sockets is not yet
complete, and will be done in a future CL.
Major differences from VFS1 gofer client (sentry/fs/gofer), with varying levels
of backportability:
- "Cache policies" are replaced by InteropMode, which control the behavior of
timestamps in addition to caching. Under InteropModeExclusive (analogous to
cacheAll) and InteropModeWritethrough (analogous to cacheAllWritethrough),
client timestamps are *not* written back to the server (it is not possible in
9P or Linux for clients to set ctime, so writing back client-authoritative
timestamps results in incoherence between atime/mtime and ctime). Under
InteropModeShared (analogous to cacheRemoteRevalidating), client timestamps
are not used at all (remote filesystem clocks are authoritative). cacheNone
is translated to InteropModeShared + new option
filesystemOptions.specialRegularFiles.
- Under InteropModeShared, "unstable attribute" reloading for permission
checks, lookup, and revalidation are fused, which is feasible in VFS2 since
gofer.filesystem controls path resolution. This results in a ~33% reduction
in RPCs for filesystem operations compared to cacheRemoteRevalidating. For
example, consider stat("/foo/bar/baz") where "/foo/bar/baz" fails
revalidation, resulting in the instantiation of a new dentry:
VFS1 RPCs:
getattr("/") // fs.MountNamespace.FindLink() => fs.Inode.CheckPermission() => gofer.inodeOperations.check() => gofer.inodeOperations.UnstableAttr()
walkgetattr("/", "foo") = fid1 // fs.Dirent.walk() => gofer.session.Revalidate() => gofer.cachePolicy.Revalidate()
clunk(fid1)
getattr("/foo") // CheckPermission
walkgetattr("/foo", "bar") = fid2 // Revalidate
clunk(fid2)
getattr("/foo/bar") // CheckPermission
walkgetattr("/foo/bar", "baz") = fid3 // Revalidate
clunk(fid3)
walkgetattr("/foo/bar", "baz") = fid4 // fs.Dirent.walk() => gofer.inodeOperations.Lookup
getattr("/foo/bar/baz") // linux.stat() => gofer.inodeOperations.UnstableAttr()
VFS2 RPCs:
getattr("/") // gofer.filesystem.walkExistingLocked()
walkgetattr("/", "foo") = fid1 // gofer.filesystem.stepExistingLocked()
clunk(fid1)
// No getattr: walkgetattr already updated metadata for permission check
walkgetattr("/foo", "bar") = fid2
clunk(fid2)
walkgetattr("/foo/bar", "baz") = fid3
// No clunk: fid3 used for new gofer.dentry
// No getattr: walkgetattr already updated metadata for stat()
- gofer.filesystem.unlinkAt() does not require instantiation of a dentry that
represents the file to be deleted. Updates #898.
- gofer.regularFileFD.OnClose() skips Tflushf for regular files under
InteropModeExclusive, as it's nonsensical to request a remote file flush
without flushing locally-buffered writes to that remote file first.
- Symlink targets are cached when InteropModeShared is not in effect.
- p9.QID.Path (which is already required to be unique for each file within a
server, and is accordingly already synthesized from device/inode numbers in
all known gofers) is used as-is for inode numbers, rather than being mapped
along with attr.RDev in the client to yet another synthetic inode number.
- Relevant parts of fsutil.CachingInodeOperations are inlined directly into
gofer package code. This avoids having to duplicate part of its functionality
in fsutil.HostMappable.
PiperOrigin-RevId: 293190213
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