update test and fix error checking

Author: simonpintarelli

ci/tests.bats

@@ -55,6 +55,20 @@ function teardown() {
     run squashfs-mount ${SQFSDIR}/tools-offset.sqfs@2048:/user-tools -- cat /user-tools/tools/fileB.txt
 }
 
+@test "mount_offset_image_neg_offset" {
+    # offset must be > 0
+    run squashfs-mount ${SQFSDIR}/tools-offset.sqfs@-2048434:/user-tools -- cat /user-tools/tools/fileB.txt
+    assert_failure
+    assert_line  --regexp ".*offset.* must be >0: .*"
+}
+
+@test "mount_offset_image_offset_twice" {
+    # only one @<offset> is allowed
+    run squashfs-mount ${SQFSDIR}/tools-offset.sqfs@2@2:/user-tools -- cat /user-tools/tools/fileB.txt
+    assert_failure
+    assert_line  --regexp ".*invalid format: .*"
+}
+
 @test "mount_images" {
     run squashfs-mount ${SQFSDIR}/binaries.sqfs:/user-environment ${SQFSDIR}/profilers.sqfs:/user-profilers ${SQFSDIR}/tools.sqfs:/user-tools -- cat /user-environment/spack-install/fileA.txt
 }

squashfs-mount.c

@@ -195,20 +195,21 @@ static mount_entry_t *parse_mount_entries(const char **argv, int argc) {
     }
     // if @offset is present, attempt to parse offset
     if ((offset_str = strtok(NULL, "@"))) {
-      char *endptr;
       // check if value is negative
-      if (strtoll(offset_str, NULL, 10) < 0) {
-        errx(EXIT_FAILURE, "invalid value in offset: %s", argv[i]);
+      long long _f;
+      if ((_f = strtoll(offset_str, NULL, 10)) < 0) {
+        errx(EXIT_FAILURE, "offset (=%lld) must be >0: %s", _f, argv[i]);
       }
       // parse offset
+      char *endptr;
       offset = strtoul(offset_str, &endptr, 10);
-      if (errno != 0 || *endptr != '\0') {
-        errx(EXIT_FAILURE, "invalid value in offset: %s", argv[i]);
+      if (*endptr != '\0') {
+        errx(EXIT_FAILURE, "invalid value in offset: %s from %s", offset_str, argv[i]);
+      }
+      // expect file_and_offset only contains one `@`
+      if (strtok(NULL, "@")) {
+        errx(EXIT_FAILURE, "invalid format: %s", argv[i]);
       }
-    }
-    // expect file_and_offset only contains one `@`
-    if (strtok(NULL, "@")) {
-      errx(EXIT_FAILURE, "invalid format %s", argv[i]);
     }
 
     strcpy(mount_entries[i].squashfs_file, file);