tarfs: Support tar files which include file modes with permissions.

[des]

Summary

Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.

[kib]

sys/fs/tarfs/tarfs_vfsops.c

518

[stevek]

sys/fs/tarfs/tarfs_vfsops.c

521

I'm still not sure what the intention is to just make it user-readable.
It has long been the behavior of tar to just ignore the flags it doesn't recognize. If the permission bits are valid, then why not use them? Additional flags would be augmentations outside of the permissions.

I think you should just be able to do:

        if (num & ~ALLPERMS != 0) {
		TARFS_DPF(ALLOC, "%s: invalid file mode at %zu\n",
		    __func__, TARFS_BLOCKSIZE * (blknum - 1));
        }
        mode = num & ALLPERMS;

[stevek]

sys/fs/tarfs/tarfs_vfsops.c

521

Also, it would be good in the log message to print the mode value that you did get.

[kib]

sys/fs/tarfs/tarfs_vfsops.c

521

It is extra annoying when untarring results in weird permissions. Having it auto-corrected at least for tarfs so that root is not needed to read weird archives is only good IMO.

[des]

sys/fs/tarfs/tarfs_vfsops.c

521

I'd argue that you shouldn't be mounting “weird archives” and if you do (which requires root privileges) and get unexpected results you can simply inspect the tar file using... tar.

[sjg]

sys/fs/tarfs/tarfs_vfsops.c

521

I agree; forcing just S_IRUSR is useless.
masking perms makes far more sense.