lib/loopdev: cosmetic changes to LOOP_CONFIGURE

Signed-off-by: Karel Zak <kzak@redhat.com>

include/loopdev.h

@@ -67,7 +67,10 @@ struct loop_info64 {
 };
 
 #ifndef LOOP_CONFIGURE
-#define LOOP_CONFIGURE 0x4C0A
+/*
+ * Since Linux v5.8-rc1 (commit 3448914e8cc550ba792d4ccc74471d1ca4293aae)
+ */
+# define LOOP_CONFIGURE		0x4C0A
 struct loop_config {
   uint32_t fd;
   uint32_t block_size;

lib/loopdev.c

@@ -1335,32 +1335,33 @@ int loopcxt_setup_device(struct loopdev_cxt *lc)
 
 	DBG(SETUP, ul_debugobj(lc, "device open: OK"));
 
+	/*
+	 * Atomic way to configure all by one ioctl call
+	 * -- since Linux v5.8-rc1, commit 3448914e8cc550ba792d4ccc74471d1ca4293aae
+	 */
 	lc->config.fd = file_fd;
 	if (ioctl(dev_fd, LOOP_CONFIGURE, &lc->config) < 0) {
 		rc = -errno;
 		errsv = errno;
-		if (errno != EINVAL)
-		{
+		if (errno != EINVAL) {
 			DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE failed: %m"));
 			goto err;
 		}
 		fallback = 1;
-	}
-	else
-	{
+	} else {
 		if (lc->blocksize > 0
 			&& (rc = loopcxt_ioctl_blocksize(lc, lc->blocksize)) < 0) {
 			errsv = -rc;
 			goto err;
 		}
-
 		DBG(SETUP, ul_debugobj(lc, "LOOP_CONFIGURE: OK"));
 	}
 
+	/*
+	 * Old deprecated way; first assign backing file FD and then in the
+	 * second step set loop device properties.
+	 */
 	if (fallback) {
-		/*
-		 * Set FD
-		 */
 		if (ioctl(dev_fd, LOOP_SET_FD, file_fd) < 0) {
 			rc = -errno;
 			errsv = errno;
@@ -1382,6 +1383,7 @@ int loopcxt_setup_device(struct loopdev_cxt *lc)
 			if (again)
 				xusleep(250000);
 		} while (again);
+
 		if (err) {
 			rc = -errno;
 			errsv = errno;