udf: refactor VRS descriptor identification

Extract code that parses a Volume Recognition Sequence descriptor
(component), in preparation for calling it twice against different
locations in a block.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Link: https://lore.kernel.org/r/20190711133852.16887-1-steve@digidescorp.com
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/udf/super.c b/fs/udf/super.c
index a143461..14a9195 100644 (file)
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -646,16 +646,67 @@ out_unlock:
        return error;
 }
 
-/* Check Volume Structure Descriptors (ECMA 167 2/9.1) */
-/* We also check any "CD-ROM Volume Descriptor Set" (ECMA 167 2/8.3.1) */
-static loff_t udf_check_vsd(struct super_block *sb)
+/*
+ * Check VSD descriptor. Returns -1 in case we are at the end of volume
+ * recognition area, 0 if the descriptor is valid but non-interesting, 1 if
+ * we found one of NSR descriptors we are looking for.
+ */
+static int identify_vsd(const struct volStructDesc *vsd)
+{
+       int ret = 0;
+
+       if (!memcmp(vsd->stdIdent, VSD_STD_ID_CD001, VSD_STD_ID_LEN)) {
+               switch (vsd->structType) {
+               case 0:
+                       udf_debug("ISO9660 Boot Record found\n");
+                       break;
+               case 1:
+                       udf_debug("ISO9660 Primary Volume Descriptor found\n");
+                       break;
+               case 2:
+                       udf_debug("ISO9660 Supplementary Volume Descriptor found\n");
+                       break;
+               case 3:
+                       udf_debug("ISO9660 Volume Partition Descriptor found\n");
+                       break;
+               case 255:
+                       udf_debug("ISO9660 Volume Descriptor Set Terminator found\n");
+                       break;
+               default:
+                       udf_debug("ISO9660 VRS (%u) found\n", vsd->structType);
+                       break;
+               }
+       } else if (!memcmp(vsd->stdIdent, VSD_STD_ID_BEA01, VSD_STD_ID_LEN))
+               ; /* ret = 0 */
+       else if (!memcmp(vsd->stdIdent, VSD_STD_ID_NSR02, VSD_STD_ID_LEN))
+               ret = 1;
+       else if (!memcmp(vsd->stdIdent, VSD_STD_ID_NSR03, VSD_STD_ID_LEN))
+               ret = 1;
+       else if (!memcmp(vsd->stdIdent, VSD_STD_ID_BOOT2, VSD_STD_ID_LEN))
+               ; /* ret = 0 */
+       else if (!memcmp(vsd->stdIdent, VSD_STD_ID_CDW02, VSD_STD_ID_LEN))
+               ; /* ret = 0 */
+       else {
+               /* TEA01 or invalid id : end of volume recognition area */
+               ret = -1;
+       }
+
+       return ret;
+}
+
+/*
+ * Check Volume Structure Descriptors (ECMA 167 2/9.1)
+ * We also check any "CD-ROM Volume Descriptor Set" (ECMA 167 2/8.3.1)
+ * @return   1 if NSR02 or NSR03 found,
+ *         -1 if first sector read error, 0 otherwise
+ */
+static int udf_check_vsd(struct super_block *sb)
 {
        struct volStructDesc *vsd = NULL;
        loff_t sector = VSD_FIRST_SECTOR_OFFSET;
        int sectorsize;
        struct buffer_head *bh = NULL;
-       int nsr02 = 0;
-       int nsr03 = 0;
+       int nsr = 0;
        struct udf_sb_info *sbi;
 
        sbi = UDF_SB(sb);
@@ -679,71 +730,20 @@ static loff_t udf_check_vsd(struct super_block *sb)
         * activity. This actually happened with uninitialised SSD partitions
         * (all 0xFF) before the check for the limit and all valid IDs were
         * added */
-       for (; !nsr02 && !nsr03 && sector < VSD_MAX_SECTOR_OFFSET;
-            sector += sectorsize) {
+       for (; !nsr && sector < VSD_MAX_SECTOR_OFFSET; sector += sectorsize) {
                /* Read a block */
                bh = udf_tread(sb, sector >> sb->s_blocksize_bits);
                if (!bh)
                        break;
 
-               /* Look for ISO  descriptors */
                vsd = (struct volStructDesc *)(bh->b_data +
                                              (sector & (sb->s_blocksize - 1)));
-
-               if (!strncmp(vsd->stdIdent, VSD_STD_ID_CD001,
-                                   VSD_STD_ID_LEN)) {
-                       switch (vsd->structType) {
-                       case 0:
-                               udf_debug("ISO9660 Boot Record found\n");
-                               break;
-                       case 1:
-                               udf_debug("ISO9660 Primary Volume Descriptor found\n");
-                               break;
-                       case 2:
-                               udf_debug("ISO9660 Supplementary Volume Descriptor found\n");
-                               break;
-                       case 3:
-                               udf_debug("ISO9660 Volume Partition Descriptor found\n");
-                               break;
-                       case 255:
-                               udf_debug("ISO9660 Volume Descriptor Set Terminator found\n");
-                               break;
-                       default:
-                               udf_debug("ISO9660 VRS (%u) found\n",
-                                         vsd->structType);
-                               break;
-                       }
-               } else if (!strncmp(vsd->stdIdent, VSD_STD_ID_BEA01,
-                                   VSD_STD_ID_LEN))
-                       ; /* nothing */
-               else if (!strncmp(vsd->stdIdent, VSD_STD_ID_TEA01,
-                                   VSD_STD_ID_LEN)) {
-                       brelse(bh);
-                       break;
-               } else if (!strncmp(vsd->stdIdent, VSD_STD_ID_NSR02,
-                                   VSD_STD_ID_LEN))
-                       nsr02 = sector;
-               else if (!strncmp(vsd->stdIdent, VSD_STD_ID_NSR03,
-                                   VSD_STD_ID_LEN))
-                       nsr03 = sector;
-               else if (!strncmp(vsd->stdIdent, VSD_STD_ID_BOOT2,
-                                   VSD_STD_ID_LEN))
-                       ; /* nothing */
-               else if (!strncmp(vsd->stdIdent, VSD_STD_ID_CDW02,
-                                   VSD_STD_ID_LEN))
-                       ; /* nothing */
-               else {
-                       /* invalid id : end of volume recognition area */
-                       brelse(bh);
-                       break;
-               }
+               nsr = identify_vsd(vsd);
                brelse(bh);
        }
 
-       if (nsr03)
-               return nsr03;
-       else if (nsr02)
-               return nsr02;
+       if (nsr > 0)
+               return 1;
        else if (!bh && sector - (sbi->s_session << sb->s_blocksize_bits) ==
                        VSD_FIRST_SECTOR_OFFSET)
                return -1;
@@ -1915,7 +1915,7 @@ static int udf_load_vrs(struct super_block *sb, struct udf_options *uopt,
                        int silent, struct kernel_lb_addr *fileset)
 {
        struct udf_sb_info *sbi = UDF_SB(sb);
-       loff_t nsr_off;
+       int nsr = 0;
        int ret;
 
        if (!sb_set_blocksize(sb, uopt->blocksize)) {
@@ -1926,13 +1926,13 @@ static int udf_load_vrs(struct super_block *sb, struct udf_options *uopt,
        sbi->s_last_block = uopt->lastblock;
        if (!uopt->novrs) {
                /* Check that it is NSR02 compliant */
-               nsr_off = udf_check_vsd(sb);
-               if (!nsr_off) {
+               nsr = udf_check_vsd(sb);
+               if (!nsr) {
                        if (!silent)
                                udf_warn(sb, "No VRS found\n");
                        return -EINVAL;
                }
-               if (nsr_off == -1)
+               if (nsr == -1)
                        udf_debug("Failed to read sector at offset %d. "
                                  "Assuming open disc. Skipping validity "
                                  "check\n", VSD_FIRST_SECTOR_OFFSET);