10.10.2012 06:00, Eric W. Biederman пишет:
ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes:
"J. Bruce Fields" <bfields@xxxxxxxxxxxx> writes:
On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
"Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> writes:
On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
Cc'ing Eric since I seem to recall he suggested doing it this way?
Yes. On second look setting fs->root won't work. We need to change fs.
The problem is that by default all kernel threads share fs so changing
fs->root will have non-local consequences.
Oh, huh. And we can't "unshare" it somehow?
I don't fully understand how nfs uses kernel threads and work queues.
My general understanding is work queues reuse their kernel threads
between different users. So it is mostly a don't pollute your
environment thing. If there was a dedicated kernel thread for each
environment this would be trivial.
What I was suggesting here is changing task->fs instead of
task->fs.root. That should just require task_lock().
Or, previously you suggested:
- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
and teach unix_bind and unix_connect how to deal with a second
type of sockaddr, AT_FD:
struct sockaddr_fd { short fd_family; short pad; int fd; }
- introduce sockaddr_unix_at that takes a directory file
descriptor as well as a unix path, and teach unix_bind and
unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
Any other options?
I am still half hoping we don't have to change the userspace API/ABI.
There is sanity checking on that path that no one seems interested in to
solve this problem.
There is a good option if we are up to userspace ABI extensions.
Implement open(2) on unix domain sockets. Where open(2) would
essentially equal connect(2) on unix domain sockets.
With an open(2) implementation we could use file_open_path and the
implementation should be pretty straight forward and maintainable.
So implementing open(2) looks like a good alternative implementation
route.
This requires patching of vfs layer as well. I don't want to say, that
the idea is not good. But it requires much more time to implement and test.
And this patch addresses the problem, which exist already and would be
great to fix it as soon as possible.
So, probably, implementing open for unix sockets is the next and more
generic step.
Thanks.
Eric
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