blktap: Move error signaling to blktapctrl

Until now the udev script for blktap devices needs to decide if to
signal success or failure to xend. As this script runs completely
independent of blktapctrl and tapdisk/ioemu which do the real work,
the udev script can't even theoretically know if tapdisk is happy.

This patch removes the udev script and replaces its checks by new
ones in libblktap.

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

2 files changed, 156 insertions, 10 deletions

diff --git a/tools/blktap/drivers/blktapctrl.c b/tools/blktap/drivers/blktapctrl.c
index 21cdfe5239..8a5630230e 100644
--- a/tools/blktap/drivers/blktapctrl.c
+++ b/tools/blktap/drivers/blktapctrl.c
@@ -659,9 +659,6 @@ static int blktapctrl_new_blkif(blkif_t *blkif)
 
 	DPRINTF("Received a poll for a new vbd\n");
 	if ( ((blk=blkif->info) != NULL) && (blk->params != NULL) ) {
-		if (blktap_interface_create(ctlfd, &major, &minor, blkif) < 0)
-			return -1;
-
 		if (test_path(blk->params, &ptr, &type, &exist, &use_ioemu) != 0) {
                         DPRINTF("Error in blktap device string(%s).\n",
                                 blk->params);
@@ -685,10 +682,6 @@ static int blktapctrl_new_blkif(blkif_t *blkif)
 			blkif->fds[WRITE] = exist->fds[WRITE];
 		}
 
-		add_disktype(blkif, type);
-		blkif->major = major;
-		blkif->minor = minor;
-
 		image = (image_t *)malloc(sizeof(image_t));
 		blkif->prv = (void *)image;
 		blkif->ops = &tapdisk_ops;
@@ -712,11 +705,18 @@ static int blktapctrl_new_blkif(blkif_t *blkif)
 			goto fail;
 		}
 
+		if (blktap_interface_create(ctlfd, &major, &minor, blkif) < 0)
+			return -1;
+
+		blkif->major = major;
+		blkif->minor = minor;
+
+		add_disktype(blkif, type);
+
 	} else return -1;
 
 	return 0;
 fail:
-	ioctl(ctlfd, BLKTAP_IOCTL_FREEINTF, minor);
 	return -EINVAL;
 }
 
diff --git a/tools/blktap/lib/xenbus.c b/tools/blktap/lib/xenbus.c
index 4fc56d661b..bf17d0b7a0 100644
--- a/tools/blktap/lib/xenbus.c
+++ b/tools/blktap/lib/xenbus.c
@@ -48,6 +48,7 @@
 #include <poll.h>
 #include <time.h>
 #include <sys/time.h>
+#include <unistd.h>
 #include "blktaplib.h"
 #include "list.h"
 #include "xs_api.h"
@@ -149,6 +150,137 @@ static int backend_remove(struct xs_handle *h, struct backend_info *be)
 	return 0;
 }
 
+static int check_sharing(struct xs_handle *h, struct backend_info *be)
+{
+	char *dom_uuid;
+	char *cur_dom_uuid;
+	char *path;
+	char *mode;
+	char *params;
+	char **domains;
+	char **devices;
+	int i, j;
+	unsigned int num_dom, num_dev;
+	blkif_info_t *info;
+	int ret = 0;
+
+	/* If the mode contains '!' or doesn't contain 'w' don't check anything */
+	xs_gather(h, be->backpath, "mode", NULL, &mode, NULL);
+	if (strchr(mode, '!'))
+		goto out;
+	if (strchr(mode, 'w') == NULL)
+		goto out;
+
+	/* Get the UUID of the domain we want to attach to */
+	if (asprintf(&path, "/local/domain/%ld", be->frontend_id) == -1)
+		goto fail;
+	xs_gather(h, path, "vm", NULL, &dom_uuid, NULL);
+	free(path);
+
+	/* Iterate through the devices of all VMs */
+	domains = xs_directory(h, XBT_NULL, "backend/tap", &num_dom);
+	if (domains == NULL)
+		num_dom = 0;
+
+	for (i = 0; !ret && (i < num_dom); i++) {
+
+		/* If it's the same VM, no action needed */
+		if (asprintf(&path, "/local/domain/%s", domains[i]) == -1) {
+			ret = -1;
+			break;
+		}
+		xs_gather(h, path, "vm", NULL, &cur_dom_uuid, NULL);
+		free(path);
+
+		if (!strcmp(cur_dom_uuid, dom_uuid)) {
+			free(cur_dom_uuid);
+			continue;
+		}
+
+		/* Check the devices */
+		if (asprintf(&path, "backend/tap/%s", domains[i]) == -1) {
+			ret = -1;
+			free(cur_dom_uuid);
+			break;
+		}
+		devices = xs_directory(h, XBT_NULL, path, &num_dev);
+		if (devices == NULL)
+			num_dev = 0;
+		free(path);
+
+		for (j = 0; !ret && (j < num_dev); j++) {
+			if (asprintf(&path, "backend/tap/%s/%s", domains[i], devices[j]) == -1) {
+				ret = -1;
+				break;
+			}
+			xs_gather(h, path, "params", NULL, &params, NULL);
+			free(path);
+
+			info =  be->blkif->info;
+			if (strcmp(params, info->params)) {
+				ret = -1;
+			}
+
+			free(params);
+		}
+
+		free(cur_dom_uuid);
+		free(devices);
+	}
+	free(domains);
+	free(dom_uuid);
+	goto out;
+
+fail:
+	ret = -1;
+out:
+	free(mode);
+	return ret;
+}
+
+static int check_image(struct xs_handle *h, struct backend_info *be,
+	const char** errmsg)
+{
+	const char *tmp;
+	const char *path;
+	int mode;
+	blkif_t *blkif = be->blkif;
+	blkif_info_t *info = blkif->info;
+
+	/* Strip off the image type */
+	path = info->params;
+
+	if (!strncmp(path, "tapdisk:", strlen("tapdisk:"))) {
+		path += strlen("tapdisk:");
+	} else if (!strncmp(path, "ioemu:", strlen("ioemu:"))) {
+		path += strlen("ioemu:");
+	}
+
+	tmp = strchr(path, ':');
+	if (tmp != NULL)
+		path = tmp + 1;
+
+	/* Check if the image exists and access is permitted */
+	mode = R_OK;
+	if (!be->readonly)
+		mode |= W_OK;
+	if (access(path, mode)) {
+		if (errno == ENOENT)
+			*errmsg = "File not found.";
+		else
+			*errmsg = "Insufficient file permissions.";
+		return -1;
+	}
+
+	/* Check that the image is not attached to a different VM */
+	if (check_sharing(h, be)) {
+		*errmsg = "File already in use by other domain";
+		return -1;
+	}
+
+	return 0;
+}
+
 static void ueblktap_setup(struct xs_handle *h, char *bepath)
 {
 	struct backend_info *be;
@@ -156,6 +288,7 @@ static void ueblktap_setup(struct xs_handle *h, char *bepath)
 	int len, er, deverr;
 	long int pdev = 0, handle;
 	blkif_info_t *blk;
+	const char* errmsg = NULL;
 	
 	be = be_lookup_be(bepath);
 	if (be == NULL)
@@ -211,6 +344,9 @@ static void ueblktap_setup(struct xs_handle *h, char *bepath)
 			be->pdev = pdev;
 		}
 
+		if (check_image(h, be, &errmsg))
+			goto fail;
+
 		er = blkif_init(be->blkif, handle, be->pdev, be->readonly);
 		if (er != 0) {
 			DPRINTF("Unable to open device %s\n",blk->params);
@@ -246,12 +382,21 @@ static void ueblktap_setup(struct xs_handle *h, char *bepath)
 	}
 
 	be->blkif->state = CONNECTED;
+	xs_printf(h, be->backpath, "hotplug-status", "connected");
+
 	DPRINTF("[SETUP] Complete\n\n");
 	goto close;
 	
 fail:
-	if ( (be != NULL) && (be->blkif != NULL) ) 
+	if (be) {
+		if (errmsg == NULL)
+			errmsg = "Setting up the backend failed. See the log "
+				"files in /var/log/xen/ for details.";
+		xs_printf(h, be->backpath, "hotplug-error", errmsg);
+		xs_printf(h, be->backpath, "hotplug-status", "error");
+
 		backend_remove(h, be);
+	}
 close:
 	if (path)
 		free(path);
@@ -286,7 +431,8 @@ static void ueblktap_probe(struct xs_handle *h, struct xenbus_watch *w,
 	len = strsep_len(bepath, '/', 7);
 	if (len < 0) 
 		goto free_be;
-	bepath[len] = '\0';
+	if (bepath[len] != '\0')
+		goto free_be;
 	
 	be = malloc(sizeof(*be));
 	if (!be) {