btrfs-show-super: don't try to print not-superblocks

If we point btrfs-show-super at a not-btrfs-device and
try to print all superblocks, bad things are apt to happen:

superblock: bytenr=274877906944, device=/dev/sdc2
---------------------------------------------------------
btrfs-show-super: ctree.h:1984: btrfs_super_csum_size: \
Assertion `!(t >= (sizeof(btrfs_csum_sizes) / sizeof((btrfs_csum_sizes)[0])))' failed.
csum			0xAborted

Don't try to print superblocks that don't look like superblocks,
and add an "-f" (force) option to try anyway, if the user
really wants to give it a shot.

Fix some spelling & capitalization while we're at it.

The manpage says that if any problem happens, 1 will
be returned, but that's already not true today LOL, so
I didn't bother to make it true when we detect bad
sb magic, either...

I figure it's worth continuing and trying all superblocks
in case just one has a corrupt magic.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
[renamed -f to -F due to clash with existing option, converted
relevant docs to asciidoc]
Signed-off-by: David Sterba <dsterba@suse.cz>

diff --git a/Documentation/btrfs-show-super.txt b/Documentation/btrfs-show-super.txt
index e06157f..62da625 100644 (file)
--- a/Documentation/btrfs-show-super.txt
+++ b/Documentation/btrfs-show-super.txt
@@ -31,6 +31,10 @@ Specify which mirror to print out.
 <super_mirror> is between 0 and 2.
 If several '-i <super_mirror>' are given, only the last one is valid.
 
+-F::
+Attempt to print the superblock even if no superblock magic is found.  May end
+badly.
+
 EXIT STATUS
 -----------
 *btrfs-show-super* will return 0 if no error happened.

diff --git a/btrfs-show-super.c b/btrfs-show-super.c
index c2ad332..ed0311f 100644 (file)
--- a/btrfs-show-super.c
+++ b/btrfs-show-super.c
@@ -40,16 +40,17 @@
 static void print_usage(void);
 static void dump_superblock(struct btrfs_super_block *sb, int full);
 int main(int argc, char **argv);
-static int load_and_dump_sb(char *, int fd, u64 sb_bytenr, int full);
+static int load_and_dump_sb(char *, int fd, u64 sb_bytenr, int full, int force);
 
 
 static void print_usage(void)
 {
        fprintf(stderr,
-               "usage: btrfs-show-super [-i super_mirror|-a|-f] dev [dev..]\n");
+               "usage: btrfs-show-super [-i super_mirror|-a|-f|-F] dev [dev..]\n");
        fprintf(stderr, "\t-f : print full superblock information\n");
        fprintf(stderr, "\t-a : print information of all superblocks\n");
        fprintf(stderr, "\t-i <super_mirror> : specify which mirror to print out\n");
+       fprintf(stderr, "\t-F : attempt to dump superblocks with bad magic\n");
        fprintf(stderr, "%s\n", BTRFS_BUILD_VERSION);
 }
 
@@ -58,13 +59,14 @@ int main(int argc, char **argv)
        int opt;
        int all = 0;
        int full = 0;
+       int force = 0;
        char *filename;
        int fd = -1;
        int i;
        u64 arg;
        u64 sb_bytenr = btrfs_sb_offset(0);
 
-       while ((opt = getopt(argc, argv, "fai:")) != -1) {
+       while ((opt = getopt(argc, argv, "fFai:")) != -1) {
                switch (opt) {
                case 'i':
                        arg = arg_strtou64(optarg);
@@ -84,6 +86,9 @@ int main(int argc, char **argv)
                case 'f':
                        full = 1;
                        break;
+               case 'F':
+                       force = 1;
+                       break;
                default:
                        print_usage();
                        exit(1);
@@ -108,7 +113,7 @@ int main(int argc, char **argv)
                        for (idx = 0; idx < BTRFS_SUPER_MIRROR_MAX; idx++) {
                                sb_bytenr = btrfs_sb_offset(idx);
                                if (load_and_dump_sb(filename, fd,
-                                                       sb_bytenr, full)) {
+                                               sb_bytenr, full, force)) {
                                        close(fd);
                                        exit(1);
                                }
@@ -116,7 +121,7 @@ int main(int argc, char **argv)
                                putchar('\n');
                        }
                } else {
-                       load_and_dump_sb(filename, fd, sb_bytenr, full);
+                       load_and_dump_sb(filename, fd, sb_bytenr, full, force);
                        putchar('\n');
                }
                close(fd);
@@ -125,7 +130,8 @@ int main(int argc, char **argv)
        exit(0);
 }
 
-static int load_and_dump_sb(char *filename, int fd, u64 sb_bytenr, int full)
+static int load_and_dump_sb(char *filename, int fd, u64 sb_bytenr, int full,
+               int force)
 {
        u8 super_block_data[BTRFS_SUPER_INFO_SIZE];
        struct btrfs_super_block *sb;
@@ -150,7 +156,13 @@ static int load_and_dump_sb(char *filename, int fd, u64 sb_bytenr, int full)
        }
        printf("superblock: bytenr=%llu, device=%s\n", sb_bytenr, filename);
        printf("---------------------------------------------------------\n");
-       dump_superblock(sb, full);
+       if (btrfs_super_magic(sb) != BTRFS_MAGIC && !force) {
+               fprintf(stderr,
+                   "ERROR: bad magic on superblock on %s at %llu\n",
+                   filename, (unsigned long long)sb_bytenr);
+       } else {
+               dump_superblock(sb, full);
+       }
        return 0;
 }