mke2fs: add support to create the file system at an offset

This can be useful when creating a disk image for virtual machines.

Addresses-Debian-Bug: #497984

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
index fea50da..6e1121e 100644 (file)
--- a/misc/mke2fs.8.in
+++ b/misc/mke2fs.8.in
@@ -246,6 +246,10 @@ parity disk, so N will be the number of disks in the array minus 1).
 This allows the block allocator to prevent read-modify-write of the
 parity in a RAID stripe if possible when the data is written.
 .TP
+.BI offset= offset
+Create the filesystem at an offset from the beginning of the device or
+file.  This can be useful when creating disk images for virtual machines.
+.TP
 .BI resize= max-online-resize
 Reserve enough space so that the block group descriptor table can grow
 to support a filesystem that has

diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index 2e8ba60..10d3211 100644 (file)
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -96,6 +96,7 @@ static int    lazy_itable_init;
 static char    *bad_blocks_filename = NULL;
 static __u32   fs_stride;
 static int     quotatype = -1;  /* Initialize both user and group quotas by default */
+static __u64   offset;
 
 static struct ext2_super_block fs_param;
 static char *fs_uuid = NULL;
@@ -710,6 +711,19 @@ static void parse_extended_opts(struct ext2_super_block *param,
                                continue;
                        }
                        param->s_desc_size = desc_size;
+               } else if (strcmp(token, "offset") == 0) {
+                       if (!arg) {
+                               r_usage++;
+                               badopt = token;
+                               continue;
+                       }
+                       offset = strtoull(arg, &p, 0);
+                       if (*p) {
+                               fprintf(stderr, _("Invalid offset: %s\n"),
+                                       arg);
+                               r_usage++;
+                               continue;
+                       }
                } else if (strcmp(token, "mmp_update_interval") == 0) {
                        if (!arg) {
                                r_usage++;
@@ -879,8 +893,10 @@ static void parse_extended_opts(struct ext2_super_block *param,
                        "and may take an argument which\n"
                        "\tis set off by an equals ('=') sign.\n\n"
                        "Valid extended options are:\n"
+                       "\tmmp_update_interval=<interval>\n"
                        "\tstride=<RAID per-disk data chunk in blocks>\n"
                        "\tstripe-width=<RAID stride * data disks in blocks>\n"
+                       "\toffset=<offset to create the file system>\n"
                        "\tresize=<resize maximum size in blocks>\n"
                        "\tlazy_itable_init=<0 to disable, 1 to enable>\n"
                        "\tlazy_journal_init=<0 to disable, 1 to enable>\n"
@@ -2368,7 +2384,7 @@ int main (int argc, char *argv[])
        int             flags;
        int             old_bitmaps;
        io_manager      io_ptr;
-       char            tdb_string[40];
+       char            opt_string[40];
        char            *hash_alg_str;
        int             itable_zeroed = 0;
 
@@ -2438,9 +2454,13 @@ int main (int argc, char *argv[])
                }
        }
 
-       sprintf(tdb_string, "tdb_data_size=%d", fs->blocksize <= 4096 ?
+       sprintf(opt_string, "tdb_data_size=%d", fs->blocksize <= 4096 ?
                32768 : fs->blocksize * 8);
-       io_channel_set_options(fs->io, tdb_string);
+       io_channel_set_options(fs->io, opt_string);
+       if (offset) {
+               sprintf(opt_string, "offset=%llu", offset);
+               io_channel_set_options(fs->io, opt_string);
+       }
 
        if (fs_param.s_flags & EXT2_FLAGS_TEST_FILESYS)
                fs->super->s_flags |= EXT2_FLAGS_TEST_FILESYS;