David Howells <dhowells@xxxxxxxxxx> writes:
> One thing that does concern me a little about bringing back the old behaviour
> for stat and *xattr is that there is no reliable way to get at the directory
> mounted directly on the mountpoint (ie. mnt_root).
>
> The problem is that:
>
> (a) you have to know to trigger the automount with some other operation first
> and
>
> (b) the other operation is not atomic wrt to the following stat/xattr, and so
> the thing mounted on the automount point may be subject to expiration and
> auto-unmounting before the second operation can proceed.
>
> I'm not sure how much of a problem these are in practice. Certainly, I'd rate
> (b) as being less serious than (a) as the expiration timeouts are generally
> quite large. (b) can be suppressed with chdir() or open() also - then you are
> forcing retension of the vfsmount.
>
> The problem can be ameliorated for such as fstatat() by passing an AT_ flag to
> either suppress automounting or to force automounting, but there aren't any
> xattr calls, for example, that take this.
>
>
> I guess it comes down to defining two things:
>
> (1) What behaviour do we actually want?
>
> (2) What departure from previous behaviour are we willing to put up with?
>
>
> On the first, I would say definitely we want mass-stat'ers (such as ls) to not
> cause mass automounting. But for ls, that has been achieved in userspace;
> there are, however, other programs to consider.
>
> I would also say that we do not want lstat(), l*xattr() and co. to cause
> automounting - but maybe they should. Perhaps if you don't want to cause
> automounting, you should explicitly pass AT_NO_AUTOMOUNT, and all path-taking
> VFS calls should have variants that accept this flag.
>
> Do we want to have guaranteed access to the root of an automounted fs? Are we
> willing to add getxattrat and similar to get it?
Perhaps we should allow getxattr and friends to work on O_PATH opens to
get the same guarantees? E.g:
fd = open(path, O_PATH);
fgetxattr(fd, ...);
This needs a patch like the following.
Miklos
----
diff --git a/fs/xattr.c b/fs/xattr.c
index f060663..6540324 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -328,7 +328,7 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
struct dentry *dentry;
int error = -EBADF;
- f = fget(fd);
+ f = fget_raw(fd);
if (!f)
return error;
dentry = f->f_path.dentry;
@@ -414,7 +414,7 @@ SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
struct file *f;
ssize_t error = -EBADF;
- f = fget(fd);
+ f = fget_raw(fd);
if (!f)
return error;
audit_inode(NULL, f->f_path.dentry);
@@ -486,7 +486,7 @@ SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
struct file *f;
ssize_t error = -EBADF;
- f = fget(fd);
+ f = fget_raw(fd);
if (!f)
return error;
audit_inode(NULL, f->f_path.dentry);
@@ -555,7 +555,7 @@ SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
struct dentry *dentry;
int error = -EBADF;
- f = fget(fd);
+ f = fget_raw(fd);
if (!f)
return error;
dentry = f->f_path.dentry;
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
