On Sat, Jun 02, 2018 at 04:09:14AM +0100, Al Viro wrote:
On Fri, Jun 01, 2018 at 09:27:43AM +0100, David Howells wrote:
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Al Viro [off-list ref] wrote:
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Instead of overloading this on open having a specific syscalls just
seems like a much saner idea.
It's not just mount API; these can be used independently of that.
Think of the uses where you pass those to ...at() and you'll see
a bunch of applications of that thing.
I kind of agree with Christoph on this point. Yes, you can use the resultant
fd for other things, but that doesn't mean it has to be obtained initially
through open() or openat() rather than, say, a new pick_mount() syscall.
Further, having more parameters available gives us the opportunity to change
the settings on any mounts we create at the point of creation.
open_subtree(int dirfd, const char *pathname, int flags), then? How would
flags be interpreted? What I see mapping at that thing is
* equivalent of O_PATH open
* clone subtree, O_PATH open root
* clone one mount, O_PATH open root
and apparently you want to add (orthogonal to that)
* make shared/slave/private/unbindable
* ditto with recursion?
* same for nodev/nosuid/noexec/noatime/nodiratime/relatime/ro/?
as well as usual AT_... flags (empty path, follow)
Choose the encoding...
_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?