Al Viro <v...@zeniv.linux.org.uk> wrote:
> 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
I would call these MOUNT_SETATTR_* rather than AT_*.
> 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)
So, I like this generally, some notes though:
I wonder if this should be two separate parameters, a mask and the settings?
I'm not sure that's worth it since some of the mask bits would cover multiple
settings.
Also, should NODIRATIME be separate from the other *ATIME flags? I do also
like treating some of these settings as enumerations rather than a set of
bits.
I would make the prototype:
int mount_setattr(int dirfd, const char *path,
unsigned int flags, unsigned int attr,
void *reserved5);
Further, do we want to say you can either change the propagation type *or*
reconfigure the mountpoint restrictions, but not both at the same time?
> With either openat() used as in this series, or explicit
> int open_tree(int dirfd, const char *path, int flags)
Maybe open_mount(), grab_mount() or pick_mount()?
I wonder if fsopen()/fspick() should be create_fs()/open_fs()...
> 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.
You also need an O_CLOEXEC equivalent.
I would make it:
OPEN_TREE_CLOEXEC 0x00000001
OPEN_TREE_EMPTY_PATH 0x00000002
OPEN_TREE_FOLLOW_SYMLINK 0x00000004
OPEN_TREE_NO_AUTOMOUNT 0x00000008
OPEN_TREE_CLONE 0x00000010
OPEN_TREE_RECURSIVE 0x00000020
adding the follow-symlinks so that you don't grab a symlink target by
accident. (Can you actually mount on top of a symlink?)
> Hell, might even add AT_UMOUNT for "open root and detach, to be dissolved on
> close", incompatible with AT_CLONE.
Cute. Guess you could do:
fd = open_mount(..., OPEN_TREE_DETACH);
mount_setattr(fd, "",
MOUNT_SETATTR_EMPTY_PATH,
MOUNT_SETATTR_NOSUID, NULL);
move_mount(fd, "", ...);
David
