An attempt to write a tool for ext4 that will allow to change inode count of a filesystem

Makefile

@@ -0,0 +1,3 @@
+all: realloc-inodes
+realloc-inodes: realloc-inodes.c
+	gcc -o realloc-inodes -lcom_err -lext2fs realloc-inodes.c

realloc-inodes.c

@@ -0,0 +1,122 @@
+/**
+ * An attempt to write a tool for ext4 that will allow to change inode count of a filesystem.
+ *
+ * In theory it shouldn't be that hard:
+ * 1) If shrinking:
+ * 1.1) move inodes so that the end of inode table is empty
+ * 1.2) mark some blocks that belonged to inode table as free
+ * 2) If growing:
+ * 2.1) move data blocks so there is enough space reserved for new inode table
+ * 2.2) mark some blocks that should belong to inode table as occupied
+ * 3) Change all inode numbers in directory entries so that
+ *    new_num = (old_num/old_inodes_per_group)*new_inodes_per_group + (old_num%inodes_per_group)
+ * 4) Change superblock: s_inodes_count, s_free_inodes_count, s_inodes_per_group
+ * 5) Change block group descriptors: bg_inode_table_(lo,hi), bg_free_inodes_count_(lo,hi),
+ *    bg_inode_bitmap_csum_(lo,hi), bg_itable_unused_(lo,hi)
+ *
+ * This is a destructive process involving metadata change so it would be good if
+ * we could first write a file containing all necessary changes, then backup all
+ * changed blocks, and then write new blocks to the disk. (maybe just use undo_io_manager?)
+ */
+
+#include <stdio.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <errno.h>
+
+#include "ext2fs/ext2_fs.h"
+#include "ext2fs/ext2fs.h"
+
+#define _(a) (a)
+
+const char *program_name = "realloc-inodes";
+
+// try to read out all directory inodes?
+void test(ext2_filsys fs)
+{
+    int i, j, retval;
+    blk64_t blk;
+    void *buf;
+    struct ext2_inode *inode;
+    retval = ext2fs_get_mem(fs->blocksize * fs->inode_blocks_per_group, &buf);
+    for (i = 0; i < fs->group_desc_count; i++)
+    {
+        // read inode table of a group
+        blk = ext2fs_inode_table_loc(fs, i);
+        retval = io_channel_read_blk64(fs->io, blk, fs->inode_blocks_per_group, buf);
+        if (retval)
+        {
+            goto errout;
+        }
+        for (j = 0; j < fs->super->s_inodes_per_group; j++)
+        {
+            inode = (struct ext2_inode*)(buf + EXT2_INODE_SIZE(fs->super) * j);
+            if (inode->i_mode & S_IFDIR)
+            {
+                
+            }
+        }
+    }
+errout:
+    ext2fs_free_mem(&buf);
+}
+
+int main(int narg, char **args)
+{
+    ext2_filsys fs;
+    io_manager io_ptr = unix_io_manager;
+    int optind, fd, retval, io_flags = 0, force = 0;
+    ext2fs_struct_stat st_buf;
+    char *device_name, *io_options;
+
+    optind = 1;
+    device_name = args[optind++];
+    add_error_table(&et_ext2_error_table);
+    fd = ext2fs_open_file(device_name, O_RDWR, 0);
+    if (fd < 0)
+    {
+        com_err("open", errno, _("while opening %s"), device_name);
+        exit(1);
+    }
+    retval = ext2fs_fstat(fd, &st_buf);
+    if (retval < 0)
+    {
+        com_err("open", errno, _("while getting stat information for %s"), device_name);
+        exit(1);
+    }
+    if (!S_ISREG(st_buf.st_mode))
+    {
+        close(fd);
+        fd = -1;
+    }
+    io_options = strchr(device_name, '?');
+    if (io_options)
+    {
+        *io_options++ = 0;
+    }
+    //io_flags = EXT2_FLAG_RW | EXT2_FLAG_EXCLUSIVE;
+    io_flags |= EXT2_FLAG_64BITS;
+    retval = ext2fs_open2(device_name, io_options, io_flags, 0, 0, io_ptr, &fs);
+    if (retval)
+    {
+        com_err(program_name, retval, _("while trying to open %s"), device_name);
+        printf(_("Couldn't find valid filesystem superblock.\n"));
+        exit(1);
+    }
+    if (!force && ((fs->super->s_state & EXT2_ERROR_FS) || ((fs->super->s_state & EXT2_VALID_FS) == 0)))
+    {
+        fprintf(stderr, _("Please run 'e2fsck -f %s' first.\n\n"), device_name);
+        exit(1);
+    }
+    test(fs);
+    ext2fs_close(fs);
+    if (fd > 0)
+    {
+        close(fd);
+    }
+}