On Mon, Sep 24, 2018 at 07:50:38AM +0100, David Howells wrote:
> Christian Brauner <christian@xxxxxxxxxx> wrote:
>
> > Ok, understood. What about passing the different attrs as a struct?
> >
> > struct mount_attr {
> > unsigned int attr_cmd,
> > unsigned int attr_values,
> > unsigned int attr_mask,
> >
> > };
> >
> > mount_setattr(int dfd, const char *path, unsigned int atflags,
> > struct mount_attr *attr);
> >
> > I find that to be a little cleaner in all honesty.
> > One could also add a version argument similar to what we currently do
> > for vfs fcaps so that kernel and userspace can easily navigate
> > compabitility when a new member gets added or removed in later releases.
>
> Yeah, we could do that - it's not like I expect mount_setattr() to have to be
> particularly performant in the user interface. I would put the attr_cmd in
> the argument list, probably, so that you can use that to vary the struct in
> future (say we run out of attribute bits).
Yes, that makes sense and mimicks standard ioctl() behavior. So
struct mount_attr {
unsigned int attr_values,
unsigned int attr_mask,
}
mount_setattr(int dfd, const char *path, unsigned int atflags,
unsigned int attr_cmd, struct mount_attr *attr);
I have thought a little more about splitting up the mount flags into
sensible sets. I think the following four sets make sense:
enum {
MOUNT_ATTR_PROPAGATION = 1,
MOUNT_ATTR_SECURITY,
MOUNT_ATTR_SYNC,
MOUNT_ATTR_TIME,
};
MOUNT_ATTR_PROPAGATION:
#define MOUNT_ATTR_PRIVATE (1<<0)
#define MOUNT_ATTR_SHARED (1<<1)
#define MOUNT_ATTR_SLAVE (1<<2)
#define MOUNT_ATTR_UNBINDABLE (1<<3)
MOUNT_ATTR_SECURITY:
#define MOUNT_ATTR_MANDLOCK (1<<0)
#define MOUNT_ATTR_NODEV (1<<1)
#define MOUNT_ATTR_NOEXEC (1<<2)
#define MOUNT_ATTR_NOSUID (1<<3)
#define MOUNT_ATTR_NOREMOTELOCK (1<<4)
#define MOUNT_ATTR_RDONLY (1<<5)
#define MOUNT_ATTR_POSIXACL (1<<6)
#define MOUNT_ATTR_SILENT (1<<7)
MOUNT_ATTR_SYNC
#define MOUNT_ATTR_DIRSYNC (1<<0)
#define MOUNT_ATTR_SYNCHRONOUS (1<<1)
MOUNT_ATTR_TIME:
#define MOUNT_ATTR_LAZYTIME (1<<0)
#define MOUNT_ATTR_NOATIME (1<<1)
#define MOUNT_ATTR_NODIRATIME (1<<2)
#define MOUNT_ATTR_RELATIME (1<<3)
#define MOUNT_ATTR_STRICTATIME (1<<4)
If we ever run out of flags in a specific set I suggest to introduce a
new enum member of the same name with a version number appended and an
alias with a (obvs lower) version number for the old set. A concrete
example would be:
enum {
MOUNT_ATTR_PROPAGATION = 1,
MOUNT_ATTR_SECURITY,
MOUNT_ATTR_SECURITY_1 = MOUNT_ATTR_SECURITY,
MOUNT_ATTR_SYNC,
MOUNT_ATTR_TIME,
MOUNT_ATTR_SECURITY_2,
};
These flags will likely become AT_* flags or be tied to a syscall
afaict.
#define MS_REMOUNT 32
#define MS_BIND 4096
#define MS_MOVE 8192
#define MS_REC 16384
Internal sb flags will not be part of the new mount attr sets. (They
should - imho - not be exposed to userspace at all.):
#define MS_KERNMOUNT (1<<22)
#define MS_SUBMOUNT (1<<26)
#define MS_NOREMOTELOCK (1<<27)
#define MS_NOSEC (1<<28)
#define MS_BORN (1<<29)
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)
What remains is an odd duck that probably could be thrown into security
but also *shrug*
#define MS_I_VERSION (1<<23)
Christian
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