debugfs: optionally create undo file

Provide the user with an option to create an undo file so that they
can roll back a failed debugfs expedition.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/debugfs/debugfs.8.in b/debugfs/debugfs.8.in
index ab6adc4..9a09cbf 100644 (file)
--- a/debugfs/debugfs.8.in
+++ b/debugfs/debugfs.8.in
@@ -31,6 +31,10 @@ request
 data_source_device
 ]
 [
+.B \-z
+.I undo_file
+]
+[
 device
 ]
 .SH DESCRIPTION
@@ -130,6 +134,16 @@ and then exit.
 print the version number of
 .B debugfs
 and exit.
+.TP
+.BI \-z " undo_file"
+Before overwriting a file system block, write the old contents of the block to
+an undo file.  This undo file can be used with e2undo(8) to restore the old
+contents of the file system should something go wrong.  If the empty string is
+passed as the undo_file argument, the undo file will be written to a file named
+resize2fs-\fIdevice\fR.e2undo in the directory specified via the
+\fIE2FSPROGS_UNDO_DIR\fR environment variable.
+
+WARNING: The undo file cannot be used to recover from a power or system crash.
 .SH SPECIFYING FILES
 Many
 .B debugfs
@@ -535,7 +549,7 @@ to those inodes.  The
 flag will enable checking the file type information in the directory
 entry to make sure it matches the inode's type.
 .TP
-.BI open " [-weficD] [-b blocksize] [-s superblock] device"
+.BI open " [-weficD] [-b blocksize] [-s superblock] [-z undo_file] device"
 Open a filesystem for editing.  The
 .I -f
 flag forces the filesystem to be opened even if there are some unknown

diff --git a/debugfs/debugfs.c b/debugfs/debugfs.c
index fe57366..4b88f73 100644 (file)
--- a/debugfs/debugfs.c
+++ b/debugfs/debugfs.c
@@ -15,6 +15,7 @@
 #include <ctype.h>
 #include <string.h>
 #include <time.h>
+#include <libgen.h>
 #ifdef HAVE_GETOPT_H
 #include <getopt.h>
 #else
@@ -48,12 +49,88 @@ ext2_filsys current_fs;
 quota_ctx_t    current_qctx;
 ext2_ino_t     root, cwd;
 
+static int debugfs_setup_tdb(const char *device_name, char *undo_file,
+                            io_manager *io_ptr)
+{
+       errcode_t retval = ENOMEM;
+       char *tdb_dir = NULL, *tdb_file = NULL;
+       char *dev_name, *tmp_name;
+       int free_tdb_dir = 0;
+
+       /* (re)open a specific undo file */
+       if (undo_file && undo_file[0] != 0) {
+               set_undo_io_backing_manager(*io_ptr);
+               *io_ptr = undo_io_manager;
+               retval = set_undo_io_backup_file(undo_file);
+               if (retval)
+                       goto err;
+               printf("Overwriting existing filesystem; this can be undone "
+                       "using the command:\n"
+                       "    e2undo %s %s\n\n",
+                       undo_file, device_name);
+               return 0;
+       }
+
+       /*
+        * Configuration via a conf file would be
+        * nice
+        */
+       tdb_dir = getenv("E2FSPROGS_UNDO_DIR");
+
+       if (tdb_dir == NULL || !strcmp(tdb_dir, "none") || (tdb_dir[0] == 0) ||
+           access(tdb_dir, W_OK)) {
+               if (free_tdb_dir)
+                       free(tdb_dir);
+               return 0;
+       }
+
+       tmp_name = strdup(device_name);
+       if (!tmp_name)
+               goto errout;
+       dev_name = basename(tmp_name);
+       tdb_file = malloc(strlen(tdb_dir) + 8 + strlen(dev_name) + 7 + 1);
+       if (!tdb_file) {
+               free(tmp_name);
+               goto errout;
+       }
+       sprintf(tdb_file, "%s/debugfs-%s.e2undo", tdb_dir, dev_name);
+       free(tmp_name);
+
+       if ((unlink(tdb_file) < 0) && (errno != ENOENT)) {
+               retval = errno;
+               goto errout;
+       }
+
+       set_undo_io_backing_manager(*io_ptr);
+       *io_ptr = undo_io_manager;
+       retval = set_undo_io_backup_file(tdb_file);
+       if (retval)
+               goto errout;
+       printf("Overwriting existing filesystem; this can be undone "
+               "using the command:\n"
+               "    e2undo %s %s\n\n", tdb_file, device_name);
+
+       if (free_tdb_dir)
+               free(tdb_dir);
+       free(tdb_file);
+       return 0;
+
+errout:
+       if (free_tdb_dir)
+               free(tdb_dir);
+       free(tdb_file);
+err:
+       com_err("debugfs", retval, "while trying to setup undo file\n");
+       return retval;
+}
+
 static void open_filesystem(char *device, int open_flags, blk64_t superblock,
                            blk64_t blocksize, int catastrophic,
-                           char *data_filename)
+                           char *data_filename, char *undo_file)
 {
        int     retval;
        io_channel data_io = 0;
+       io_manager io_ptr = unix_io_manager;
 
        if (superblock != 0 && blocksize == 0) {
                com_err(device, 0, "if you specify the superblock, you must also specify the block size");
@@ -84,8 +161,14 @@ static void open_filesystem(char *device, int open_flags, blk64_t superblock,
        if (catastrophic)
                open_flags |= EXT2_FLAG_SKIP_MMP;
 
+       if (undo_file) {
+               retval = debugfs_setup_tdb(device, undo_file, &io_ptr);
+               if (retval)
+                       exit(1);
+       }
+
        retval = ext2fs_open(device, open_flags, superblock, blocksize,
-                            unix_io_manager, &current_fs);
+                            io_ptr, &current_fs);
        if (retval) {
                com_err(device, retval, "while opening filesystem");
                if (retval == EXT2_ET_BAD_MAGIC)
@@ -136,9 +219,10 @@ void do_open_filesys(int argc, char **argv)
        blk64_t blocksize = 0;
        int     open_flags = EXT2_FLAG_SOFTSUPP_FEATURES | EXT2_FLAG_64BITS; 
        char    *data_filename = 0;
+       char    *undo_file = NULL;
 
        reset_getopt();
-       while ((c = getopt (argc, argv, "iwfecb:s:d:D")) != EOF) {
+       while ((c = getopt(argc, argv, "iwfecb:s:d:Dz:")) != EOF) {
                switch (c) {
                case 'i':
                        open_flags |= EXT2_FLAG_IMAGE_FILE;
@@ -177,6 +261,9 @@ void do_open_filesys(int argc, char **argv)
                        if (err)
                                return;
                        break;
+               case 'z':
+                       undo_file = optarg;
+                       break;
                default:
                        goto print_usage;
                }
@@ -188,7 +275,7 @@ void do_open_filesys(int argc, char **argv)
                return;
        open_filesystem(argv[optind], open_flags,
                        superblock, blocksize, catastrophic,
-                       data_filename);
+                       data_filename, undo_file);
        return;
 
 print_usage:
@@ -2219,7 +2306,7 @@ int main(int argc, char **argv)
                "Usage: %s [-b blocksize] [-s superblock] [-f cmd_file] "
                "[-R request] [-V] ["
 #ifndef READ_ONLY
-               "[-w] "
+               "[-w] [-z undo_file] "
 #endif
                "[-c] device]";
        int             c;
@@ -2234,7 +2321,8 @@ int main(int argc, char **argv)
 #ifdef READ_ONLY
        const char      *opt_string = "nicR:f:b:s:Vd:D";
 #else
-       const char      *opt_string = "niwcR:f:b:s:Vd:D";
+       const char      *opt_string = "niwcR:f:b:s:Vd:Dz:";
+       char            *undo_file = NULL;
 #endif
 
        if (debug_prog_name == 0)
@@ -2291,6 +2379,9 @@ int main(int argc, char **argv)
                        fprintf(stderr, "\tUsing %s\n",
                                error_message(EXT2_ET_BASE));
                        exit(0);
+               case 'z':
+                       undo_file = optarg;
+                       break;
                default:
                        com_err(argv[0], 0, usage, debug_prog_name);
                        return 1;
@@ -2299,7 +2390,7 @@ int main(int argc, char **argv)
        if (optind < argc)
                open_filesystem(argv[optind], open_flags,
                                superblock, blocksize, catastrophic,
-                               data_filename);
+                               data_filename, undo_file);
 
        sci_idx = ss_create_invocation(debug_prog_name, "0.0", (char *) NULL,
                                       &debug_cmds, &retval);