libmount: one iteration to detect overlap and reuse loopdev

The current code scans loopdevs to detect already used loop device and
another scan to detect overlap.

Let's use one scan only, for this purpose loopcxt_find_overlap() has
been modified to return info (rc==2) about full size and offset match.

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

1 files changed, 31 insertions, 32 deletions

diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c
index aabb2dd20..8ef183107 100644
--- a/libmount/src/context_loopdev.c
+++ b/libmount/src/context_loopdev.c
@@ -220,58 +220,53 @@ int mnt_context_setup_loopdev(struct libmnt_context *cxt)
 		if (rc)
 			goto done_no_deinit;
 
-		rc = loopcxt_find_by_backing_file(&lc,
-				backing_file, offset, sizelimit,
-				LOOPDEV_FL_OFFSET | LOOPDEV_FL_SIZELIMIT);
-		if (rc < 0)
+		rc = loopcxt_find_overlap(&lc, backing_file, offset, sizelimit);
+		switch (rc) {
+		case 0: /* not found */
+			DBG(LOOP, ul_debugobj(cxt, "not found overlaping loopdev"));
+			loopcxt_deinit(&lc);
+			break;
+
+		case 1:	/* overlap */
+			DBG(LOOP, ul_debugobj(cxt, "overlaping %s detected",
+						loopcxt_get_device(&lc)));
+			rc = -MNT_ERR_LOOPOVERLAP;
 			goto done;
-		if (rc == 0) {
+
+		case 2: /* overlap -- full size and offset match (reuse) */
+		{
 			uint32_t lc_encrypt_type;
 
-			DBG(LOOP, ul_debugobj(cxt, "using existing loop device %s",
+			DBG(LOOP, ul_debugobj(cxt, "re-using existing loop device %s",
 				loopcxt_get_device(&lc)));
 
 			/* Once a loop is initialized RO, there is no
-			   way to change its parameters. */
-			if (loopcxt_is_readonly(&lc) && !(lo_flags & LO_FLAGS_READ_ONLY)) {
+			 * way to change its parameters. */
+			if (loopcxt_is_readonly(&lc)
+			    && !(lo_flags & LO_FLAGS_READ_ONLY)) {
+				DBG(LOOP, ul_debugobj(cxt, "%s is read-only",
+						loopcxt_get_device(&lc)));
 				rc = -EROFS;
 				goto done;
 			}
 
-			/* This is no more supported, but check to be
-			 * safe. */
-			if (loopcxt_get_encrypt_type(&lc, &lc_encrypt_type)) {
-				DBG(LOOP, ul_debugobj(cxt, "failed to get crypt type for device %s",
-					loopcxt_get_device(&lc)));
-				rc = -MNT_ERR_LOOPDEV;
-				goto done;
-			}
-			if (lc_encrypt_type != LO_CRYPT_NONE) {
+			/* This is no more supported, but check to be safe. */
+			if (loopcxt_get_encrypt_type(&lc, &lc_encrypt_type) == 0
+			    && lc_encrypt_type != LO_CRYPT_NONE) {
 				DBG(LOOP, ul_debugobj(cxt, "encryption no longer supported for device %s",
 					loopcxt_get_device(&lc)));
 				rc = -MNT_ERR_LOOPOVERLAP;
 				goto done;
 			}
+			rc = 0;
 			goto success;
 		}
-		loopcxt_deinit(&lc);
-		/* No existing loop device matches. Now we need to
-		 * check that no loop device overlaps our target range
-		 * inside the backing file. */
-		rc = loopcxt_init(&lc, 0);
-		if (rc)
-			goto done_no_deinit;
-
-		rc = loopcxt_find_overlap(&lc, backing_file, offset, sizelimit);
-		if (rc < 0)
-			goto done;
-		if (rc == 0) {
-			rc = -MNT_ERR_LOOPOVERLAP;
+		default: /* error */
 			goto done;
 		}
-		loopcxt_deinit(&lc);
 	}
 
+	DBG(LOOP, ul_debugobj(cxt, "not found; create a new loop device"));
 	rc = loopcxt_init(&lc, 0);
 	if (rc)
 		goto done_no_deinit;
@@ -362,7 +357,11 @@ success:
 		 * otherwise it will be auto-cleared by kernel
 		 */
 		cxt->loopdev_fd = loopcxt_get_fd(&lc);
-		loopcxt_set_fd(&lc, -1, 0);
+		if (cxt->loopdev_fd < 0) {
+			DBG(LOOP, ul_debugobj(cxt, "failed to get loopdev FD"));
+			rc = -errno;
+		} else
+			loopcxt_set_fd(&lc, -1, 0);
 	}
 done:
 	loopcxt_deinit(&lc);