On Sat, Jun 02, 2018 at 04:42:56AM +0100, Al Viro wrote:
> _If_ I'm interpreting that correctly, that should be something like a bitmap
> of attributes to modify + values to set for each. Let's see -
> propagation 1 + 2 bits
> nodev 1 + 1
> noexec 1 + 1
> nosuid 1 + 1
> ro 1 + 1
> atime 1 + 3
> That's 15 bits. On top of that, we have 1 bit for "clone or original"
> and 1 bit for "recursive or single-mount". As well as AT_EMPTY_PATH,
> and AT_NO_AUTOMOUNT (inconvenient, since these are fixed bits). In
> principle, that does fit into int, with some space to spare...
>
> Is that what you have in mind?
TBH, I would probably prefer separate mount_setattr(2) for that kind
of work, with something like
int mount_setattr(int dirfd, const char *path, int flags, int attr)
*not* opening any files.
flags:
AT_EMPTY_PATH, AT_NO_AUTOMOUNT, AT_RECURSIVE
attr:
MOUNT_SETATTR_DEV (1<<0)
MOUNT_SETATTR_NODEV (1<<0)|(1<<1)
MOUNT_SETATTR_EXEC (1<<2)
MOUNT_SETATTR_NOEXEC (1<<2)|(1<<3)
MOUNT_SETATTR_SUID (1<<4)
MOUNT_SETATTR_NOSUID (1<<4)|(1<<5)
MOUNT_SETATTR_RW (1<<6)
MOUNT_SETATTR_RO (1<<6)|(1<<7)
MOUNT_SETATTR_RELATIME (1<<8)
MOUNT_SETATTR_NOATIME (1<<8)|(1<<9)
MOUNT_SETATTR_NODIRATIME (1<<8)|(2<<9)
MOUNT_SETATTR_STRICTATIME (1<<8)|(3<<9)
MOUNT_SETATTR_PRIVATE (1<<11)
MOUNT_SETATTR_SHARED (1<<11)|(1<<12)
MOUNT_SETATTR_SLAVE (1<<11)|(2<<12)
MOUNT_SETATTR_UNBINDABLE (1<<11)|(3<<12)
With either openat() used as in this series, or explicit
int open_tree(int dirfd, const char *path, int flags)
returning a descriptor, with flags being
AT_EMPTY_PATH, AT_NO_AUTOMOUNT, AT_RECURSIVE, AT_CLONE
with AT_RECURSIVE without AT_CLONE being an error. Hell, might
even add AT_UMOUNT for "open root and detach, to be dissolved on
close", incompatible with AT_CLONE.
Comments?
