blktapctrl: Select backend by prefix

This patch adds support for specifying the backend (tapdisk or ioemu)
to blktapctrl. Images can be specified e.g. as tap:tapdisk:aio,
tap:ioemu:qcow2 or tap:vmdk. When omitting the backend, a default is
chosen based on the image type (currently always tapdisk because ioemu
as a backend is broken until a follow-up patch series against qemu-xen
is applied)

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

2 files changed, 38 insertions, 17 deletions

diff --git a/tools/blktap/drivers/blktapctrl.c b/tools/blktap/drivers/blktapctrl.c
index b8a872bbbb..b7ee572837 100644
--- a/tools/blktap/drivers/blktapctrl.c
+++ b/tools/blktap/drivers/blktapctrl.c
@@ -148,7 +148,8 @@ static int get_tapdisk_pid(blkif_t *blkif)
  *   return 0 on success, -1 on error.
  */
 
-static int test_path(char *path, char **dev, int *type, blkif_t **blkif)
+static int test_path(char *path, char **dev, int *type, blkif_t **blkif,
+	int* use_ioemu)
 {
 	char *ptr, handle[10];
 	int i, size, found = 0;
@@ -158,6 +159,17 @@ static int test_path(char *path, char **dev, int *type, blkif_t **blkif)
 	*type = MAX_DISK_TYPES + 1;
         *blkif = NULL;
 
+	if (!strncmp(path, "tapdisk:", strlen("tapdisk:"))) {
+		*use_ioemu = 0;
+		path += strlen("tapdisk:");
+	} else if (!strncmp(path, "ioemu:", strlen("ioemu:"))) {
+		*use_ioemu = 1;
+		path += strlen("ioemu:");
+	} else {
+		// Use the default for the image type
+		*use_ioemu = -1;
+	}
+
 	if ( (ptr = strstr(path, ":"))!=NULL) {
 		handle_len = (ptr - path);
 		memcpy(handle, path, handle_len);
@@ -174,6 +186,8 @@ static int test_path(char *path, char **dev, int *type, blkif_t **blkif)
                         }
 
 			if (found) {
+				if (*use_ioemu == -1)
+					*use_ioemu = dtypes[i]->use_ioemu;
 				*type = dtypes[i]->idnum;
                         
                         if (dtypes[i]->single_handler == 1) {
@@ -185,6 +199,7 @@ static int test_path(char *path, char **dev, int *type, blkif_t **blkif)
                                         *blkif = active_disks[dtypes[i]
                                                              ->idnum]->blkif;
                         }
+
                         return 0;
                 }
             }
@@ -504,7 +519,8 @@ static int connect_qemu(blkif_t *blkif, int domid)
 	static int tapdisk_ioemu_pid = 0;
 	static int dom0_readfd = 0;
 	static int dom0_writefd = 0;
-	
+	int refresh_pid = 0;
+
 	if (asprintf(&rdctldev, BLKTAP_CTRL_DIR "/qemu-read-%d", domid) < 0)
 		return -1;
 
@@ -523,15 +539,23 @@ static int connect_qemu(blkif_t *blkif, int domid)
 		if (tapdisk_ioemu_pid == 0 || kill(tapdisk_ioemu_pid, 0)) {
 			/* No device model and tapdisk-ioemu doesn't run yet */
 			DPRINTF("Launching tapdisk-ioemu\n");
-			tapdisk_ioemu_pid = launch_tapdisk_ioemu();
+			launch_tapdisk_ioemu();
 			
 			dom0_readfd = open_ctrl_socket(wrctldev);
 			dom0_writefd = open_ctrl_socket(rdctldev);
+
+			refresh_pid = 1;
 		}
 
 		DPRINTF("Using tapdisk-ioemu connection\n");
 		blkif->fds[READ] = dom0_readfd;
 		blkif->fds[WRITE] = dom0_writefd;
+
+		if (refresh_pid) {
+			get_tapdisk_pid(blkif);
+			tapdisk_ioemu_pid = blkif->tappid;
+		}
+
 	} else if (access(rdctldev, R_OK | W_OK) == 0) {
 		/* Use existing pipe to the device model */
 		DPRINTF("Using qemu-dm connection\n");
@@ -605,13 +629,14 @@ static int blktapctrl_new_blkif(blkif_t *blkif)
 	image_t *image;
 	blkif_t *exist = NULL;
 	static uint16_t next_cookie = 0;
+	int use_ioemu;
 
 	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) != 0) {
+		if (test_path(blk->params, &ptr, &type, &exist, &use_ioemu) != 0) {
                         DPRINTF("Error in blktap device string(%s).\n",
                                 blk->params);
                         goto fail;
@@ -620,7 +645,7 @@ static int blktapctrl_new_blkif(blkif_t *blkif)
 		blkif->cookie = next_cookie++;
 
 		if (!exist) {
-			if (type == DISK_TYPE_IOEMU) {
+			if (use_ioemu) {
 				if (connect_qemu(blkif, blkif->domid))
 					goto fail;
 			} else {
diff --git a/tools/blktap/drivers/tapdisk.h b/tools/blktap/drivers/tapdisk.h
index 22450ff03b..38f3c40fa6 100644
--- a/tools/blktap/drivers/tapdisk.h
+++ b/tools/blktap/drivers/tapdisk.h
@@ -145,6 +145,8 @@ typedef struct disk_info {
 	char handle[10];     /* xend handle, e.g. 'ram' */
 	int  single_handler; /* is there a single controller for all */
 	                     /* instances of disk type? */
+	int  use_ioemu;      /* backend provider: 0 = tapdisk; 1 = ioemu */
+
 #ifdef TAPDISK
 	struct tap_disk *drv;	
 #endif
@@ -167,7 +169,6 @@ extern struct tap_disk tapdisk_qcow2;
 #define DISK_TYPE_RAM      3
 #define DISK_TYPE_QCOW     4
 #define DISK_TYPE_QCOW2    5
-#define DISK_TYPE_IOEMU    6
 
 
 /*Define Individual Disk Parameters here */
@@ -176,6 +177,7 @@ static disk_info_t aio_disk = {
 	"raw image (aio)",
 	"aio",
 	0,
+	0,
 #ifdef TAPDISK
 	&tapdisk_aio,
 #endif
@@ -186,6 +188,7 @@ static disk_info_t sync_disk = {
 	"raw image (sync)",
 	"sync",
 	0,
+	0,
 #ifdef TAPDISK
 	&tapdisk_sync,
 #endif
@@ -196,6 +199,7 @@ static disk_info_t vmdk_disk = {
 	"vmware image (vmdk)",
 	"vmdk",
 	1,
+	0,
 #ifdef TAPDISK
 	&tapdisk_vmdk,
 #endif
@@ -206,6 +210,7 @@ static disk_info_t ram_disk = {
 	"ramdisk image (ram)",
 	"ram",
 	1,
+	0,
 #ifdef TAPDISK
 	&tapdisk_ram,
 #endif
@@ -216,6 +221,7 @@ static disk_info_t qcow_disk = {
 	"qcow disk (qcow)",
 	"qcow",
 	0,
+	0,
 #ifdef TAPDISK
 	&tapdisk_qcow,
 #endif
@@ -226,21 +232,12 @@ static disk_info_t qcow2_disk = {
 	"qcow2 disk (qcow2)",
 	"qcow2",
 	0,
+	0,
 #ifdef TAPDISK
 	&tapdisk_qcow2,
 #endif
 };
 
-static disk_info_t ioemu_disk = {
-	DISK_TYPE_IOEMU,
-	"ioemu disk",
-	"ioemu",
-	1,
-#ifdef TAPDISK
-	NULL
-#endif
-};
-
 /*Main disk info array */
 static disk_info_t *dtypes[] = {
 	&aio_disk,
@@ -249,7 +246,6 @@ static disk_info_t *dtypes[] = {
 	&ram_disk,
 	&qcow_disk,
 	&qcow2_disk,
-	&ioemu_disk,
 };
 
 typedef struct driver_list_entry {