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Re: [libvirt] [Qemu-devel] [PATCH v5 6/6] block: Enable qemu_open/close to work with fd sets





On 07/26/2012 05:07 AM, Kevin Wolf wrote:
Am 26.07.2012 05:57, schrieb Corey Bryant:
On 07/25/2012 03:43 PM, Eric Blake wrote:
On 07/23/2012 07:08 AM, Corey Bryant wrote:
+int monitor_fdset_get_fd(Monitor *mon, int64_t fdset_id, int flags)
+{
+    mon_fdset_t *mon_fdset;
+    mon_fdset_fd_t *mon_fdset_fd;
+    int mon_fd_flags;
+
+    if (!mon) {
+        errno = ENOENT;
+        return -1;
+    }
+
+    QLIST_FOREACH(mon_fdset, &mon->fdsets, next) {
+        if (mon_fdset->id != fdset_id) {
+            continue;
+        }
+        QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
+            if (mon_fdset_fd->removed) {
+                continue;
+            }
+
+            mon_fd_flags = fcntl(mon_fdset_fd->fd, F_GETFL);
+            if (mon_fd_flags == -1) {
+                return -1;

This says we fail on the first fcntl() failure, instead of trying other
fds in the set.  Granted, an fcntl() failure is probably the sign of a
bigger bug (such as closing an fd at the wrong point in time), so I
guess trying to go on doesn't make much sense once we already know we
are hosed.


I think I'll stick with it the way it is.  If fcntl() fails we might
have a tainted fd set so I think we should fail.

The alternative would be s/return 1/continue/, right? I think either way
is acceptable.

+            }
+
+            switch (flags & O_ACCMODE) {
+            case O_RDWR:
+                if ((mon_fd_flags & O_ACCMODE) == O_RDWR) {
+                    return mon_fdset_fd->fd;
+                }
+                break;
+            case O_RDONLY:
+                if ((mon_fd_flags & O_ACCMODE) == O_RDONLY) {
+                    return mon_fdset_fd->fd;
+                }
+                break;

Do we want to allow the case where the caller asked for O_RDONLY, but
the set only has O_RDWR?  After all, the caller is getting a compatible
subset of what the set offers.

I don't see a problem with it.

I would require exact matches like you implemented, in order to prevent
damage if we ever had a bug that writes to a read-only file. I believe
it also makes the semantics clearer and the code simpler, while it
shouldn't make much of a difference for clients.

Kevin


Alright, then I'll plan on requiring exact matches of access mode flags.

--
Regards,
Corey



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