add virtiofs mount utility

[emil_etsalapatis.com]

Summary

Add a mount userspace utility specific to virtiofs.

[asomers]

Can you add a man page, too?

sbin/mount_virtiofs/mount_virtiofs.c

4–11

These copyright holders look copy/pasted. You should remove them.

[val_packett.cool]

Do we actually need the utility? mount.c says,

/* XXX: We need to get away from implementing external mount
 *      programs for every filesystem, and move towards having
 *	each filesystem properly implement the nmount() system call.
 */

And for tag-as-first-argument convenience (instead of specifying tag=) just take the tag as the "from"?

[emil_etsalapatis.com]

In D46297#1057513, @asomers wrote:

Can you add a man page, too?

Sounds good, I will add it in this diff if we keep the utility.

In D46297#1060015, @val_packett.cool wrote:

Do we actually need the utility? mount.c says,

/* XXX: We need to get away from implementing external mount
 *      programs for every filesystem, and move towards having
 *	each filesystem properly implement the nmount() system call.
 */

And for tag-as-first-argument convenience (instead of specifying tag=) just take the tag as the "from"?

That would be nice, I'll try out using the generic mount utility to see if we can make do without it. I made a new utility for virtiofs because I started off of the FUSE dedicated mount utility, but it turns out that virtiofs shares very little mount logic with FUSE.