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>

diff --git a/lib/loopdev.c b/lib/loopdev.c
index cb925ae8ea2b97970d0ddb40cd06991b814ea367..21c8f4366ae4473845b06329992c9c894a4c634c 100644 (file)
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -1566,7 +1566,7 @@ int loopcxt_find_by_backing_file(struct loopdev_cxt *lc, const char *filename,
 }
 
 /*
- * Returns: 0 = success, < 0 error, 1 not found
+ * Returns: 0 = not found, < 0 error, 1 found, 2 found full size and offset match
  */
 int loopcxt_find_overlap(struct loopdev_cxt *lc, const char *filename,
                           uint64_t offset, uint64_t sizelimit)
@@ -1590,7 +1590,7 @@ int loopcxt_find_overlap(struct loopdev_cxt *lc, const char *filename,
                                     filename, offset, sizelimit, 0);
                if (!rc)
                        continue;       /* unused */
-               if (rc != 1)
+               if (rc < 0)
                        break;          /* error */
 
                DBG(CXT, ul_debugobj(lc, "found %s backed by %s",
@@ -1609,15 +1609,29 @@ int loopcxt_find_overlap(struct loopdev_cxt *lc, const char *filename,
                        break;
                }
 
+               /* full match */
+               if (lc_sizelimit == sizelimit && lc_offset == offset) {
+                       DBG(CXT, ul_debugobj(lc, "overlapping loop device %s (full match)",
+                                               loopcxt_get_device(lc)));
+                       rc = 2;
+                       goto found;
+               }
+
+               /* overlap */
                if (lc_sizelimit != 0 && offset >= lc_offset + lc_sizelimit)
                        continue;
                if (sizelimit != 0 && offset + sizelimit <= lc_offset)
                        continue;
+
                DBG(CXT, ul_debugobj(lc, "overlapping loop device %s",
                        loopcxt_get_device(lc)));
-                       rc = 0;
-                       break;
+                       rc = 1;
+                       goto found;
        }
+
+       if (rc == 1)
+               rc = 0; /* not found */
+found:
        loopcxt_deinit_iterator(lc);
        return rc;
 }

diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c
index aabb2dd20fbea1581895df3ee46ec2eed82d5580..8ef183107e2b9e7cd686efdcba0efd28dc602ba3 100644 (file)
--- 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);