storage: Combine some duplicate code

Volume detection in the scsi backend was duplicating code already
present in storage_backend.c. Let's drop the duplicate code.

Also, change the shared function name to be less generic, and remove
some error squashing in the other call site.

src/storage/storage_backend.c

@@ -1050,7 +1050,7 @@ static struct diskType const disk_types[] = {
 
 
 int
-virStorageBackendUpdateVolTargetFormatFD(virStorageVolTargetPtr target,
+virStorageBackendDetectBlockVolFormatFD(virStorageVolTargetPtr target,
                                         int fd)
 {
     int i;

src/storage/storage_backend.h

@@ -92,7 +92,7 @@ int virStorageBackendUpdateVolTargetInfoFD(virStorageVolTargetPtr target,
                                            unsigned long long *allocation,
                                            unsigned long long *capacity);
 int
-virStorageBackendUpdateVolTargetFormatFD(virStorageVolTargetPtr target,
+virStorageBackendDetectBlockVolFormatFD(virStorageVolTargetPtr target,
                                         int fd);
 
 char *virStorageBackendStablePath(virStoragePoolObjPtr pool,

src/storage/storage_backend_mpath.c

@@ -59,7 +59,7 @@ virStorageBackendMpathUpdateVolTargetInfo(virStorageVolTargetPtr target,
                                                capacity) < 0)
         goto out;
 
-    if (virStorageBackendUpdateVolTargetFormatFD(target, fd) < 0)
+    if (virStorageBackendDetectBlockVolFormatFD(target, fd) < 0)
         goto out;
 
     ret = 0;

src/storage/storage_backend_scsi.c

@@ -135,10 +135,7 @@ virStorageBackendSCSIUpdateVolTargetInfo(virStorageVolTargetPtr target,
                                          unsigned long long *allocation,
                                          unsigned long long *capacity)
 {
-    int fd, i, ret = -1;
-    off_t start;
-    unsigned char buffer[1024];
-    ssize_t bytes;
+    int fd, ret = -1;
 
     if ((fd = open(target->path, O_RDONLY)) < 0) {
         virReportSystemError(errno,
@@ -153,33 +150,8 @@ virStorageBackendSCSIUpdateVolTargetInfo(virStorageVolTargetPtr target,
                                                capacity) < 0)
         goto cleanup;
 
-    /* make sure to set the target format "unknown" to begin with */
-    target->format = VIR_STORAGE_POOL_DISK_UNKNOWN;
-
-    start = lseek(fd, 0, SEEK_SET);
-    if (start < 0) {
-        virReportSystemError(errno,
-                             _("cannot seek to beginning of file '%s'"),
-                             target->path);
-        goto cleanup;
-    }
-    bytes = saferead(fd, buffer, sizeof(buffer));
-    if (bytes < 0) {
-        virReportSystemError(errno,
-                             _("cannot read beginning of file '%s'"),
-                             target->path);
+    if (virStorageBackendDetectBlockVolFormatFD(target, fd) < 0)
         goto cleanup;
-    }
-
-    for (i = 0; disk_types[i].part_table_type != -1; i++) {
-        if (disk_types[i].offset + disk_types[i].length > bytes)
-            continue;
-        if (memcmp(buffer+disk_types[i].offset, &disk_types[i].magic,
-            disk_types[i].length) == 0) {
-            target->format = disk_types[i].part_table_type;
-            break;
-        }
-    }
 
     ret = 0;