Re: [PATCH 00/19] VFS: Filesystem information and notifications [ver #16]

Hi David,

I have a few generic remarks for new syscalls...

 (3) New single-bit capability flags can be added.  This is a structure-typed
     attribute and, as such, (2) applies.  Any bits you wanted but the kernel
     doesn't support are automatically set to 0.

fsinfo() may be called like the following, for example:

	struct fsinfo_params params = {
		.at_flags	= AT_SYMLINK_NOFOLLOW,

Shouldn't all new syscalls be able to provide the RESOLVE_

Shouldn't all new syscalls be able to provide the RESOLVE_ flags
supported in openat2?

		.flags		= FSINFO_FLAGS_QUERY_PATH,
		.request	= FSINFO_ATTR_AFS_SERVER_ADDRESSES,
		.Nth		= 2,
	};
	struct fsinfo_server_address address;
	len = fsinfo(AT_FDCWD, "/afs/grand.central.org/doc", &params,
		     &address, sizeof(address));

Also passing sizeof(params) would allow future updates of fsinfo_params,
also similar to openat2(), clone3()...

========================
FILESYSTEM NOTIFICATIONS
========================

The second system call, watch_mount(), places a watch on a point in the
mount topology specified by the dirfd, path and at_flags parameters.  All
mount topology change and mount attribute change notifications in the
subtree rooted at that point can be intercepted by the watch.  Watches are
ducted through pipes:

	int fd[2];
	pipe2(fd, O_NOTIFICATION_PIPE);
	ioctl(fd[0], IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE);
	watch_mount(AT_FDCWD, "/", 0, fd[0], 0x02);

I guess similar things apply here.

Does that make sense to you?

metze