[PATCH 3/4] blktapctrl: Fix too early close of pipes

[Kevin Wolf <kwolf@suse.de>]

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Connections to ioemu have single_handler set, so they are closed as
soon as all images of a certain type are closed. This is wrong with
ioemu: All images that belong to the same domain are handled by the
same backend process (usually qemu-dm, but also tapdisk-ioemu for
domains without device model), regardless of the image type.

This patch checks for the same-domain condition for ioemu connections.

Signed-off-by: Kevin Wolf <kwolf@suse.de>

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blktapctrl: Fix too early close of pipes

Connections to ioemu have single_handler set, so they are closed as
soon as all images of a certain type are closed. This is wrong with
ioemu: All images that belong to the same domain are handled by the
same backend process (usually qemu-dm, but also tapdisk-ioemu for
domains without device model), regardless of the image type.

This patch checks for the same-domain condition for ioemu connections.

Signed-off-by: Kevin Wolf <kwolf@suse.de>

Index: xen-unstable.hg/tools/blktap/drivers/blktapctrl.c
===================================================================
--- xen-unstable.hg.orig/tools/blktap/drivers/blktapctrl.c
+++ xen-unstable.hg/tools/blktap/drivers/blktapctrl.c
@@ -231,6 +231,24 @@ static void add_disktype(blkif_t *blkif,
 	entry->pprev = pprev;
 }
 
+static int qemu_instance_has_disks(pid_t pid)
+{
+	int i;
+	int count = 0;
+	driver_list_entry_t *entry;
+
+	for (i = 0; i < MAX_DISK_TYPES; i++) {
+		entry = active_disks[i];
+		while (entry) {
+			if ((entry->blkif->tappid == pid) && dtypes[i]->use_ioemu)
+				count++;
+			entry = entry->next;
+		}
+	}
+
+	return (count != 0);
+}
+
 static int del_disktype(blkif_t *blkif)
 {
 	driver_list_entry_t *entry, **pprev;
@@ -255,6 +273,14 @@ static int del_disktype(blkif_t *blkif)
 	DPRINTF("DEL_DISKTYPE: Freeing entry\n");
 	free(entry);
 
+	/*
+	 * When using ioemu, all disks of one VM are connected to the same
+	 * qemu-dm instance. We may close the file handle only if there is
+	 * no other disk left for this domain.
+	 */
+	if (dtypes[type]->use_ioemu)
+		return !qemu_instance_has_disks(blkif->tappid);
+
 	/* Caller should close() if no single controller, or list is empty. */
 	return (!dtypes[type]->single_handler || (active_disks[type] == NULL));
 }
@@ -721,6 +747,7 @@ static int unmap_blktapctrl(blkif_t *blk
 	}
 
 	if (del_disktype(blkif)) {
+		DPRINTF("Closing communication pipe to pid %d\n", blkif->tappid);
 		close(blkif->fds[WRITE]);
 		close(blkif->fds[READ]);
 	}

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