resize2fs: enforce restrictions if the kernel doesn't do meta_bg resizing

Enhance the online resizing code to be more nuanced about resizing
restrictions.  If the kernel supports meta_bg resizing, then we can
skip all of the restrictions.  If the kernel does not support meta_bg
resizing, check more carefully to make sure there are enough reserved
gdt blocks, so that the user gets a clearer error message.

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

diff --git a/resize/online.c b/resize/online.c
index 966ea1e..d3d3546 100644 (file)
--- a/resize/online.c
+++ b/resize/online.c
@@ -56,12 +56,35 @@ errcode_t online_resize_fs(ext2_filsys fs, const char *mtpt,
                EXT2_DESC_PER_BLOCK(fs->super));
        printf("old_desc_blocks = %lu, new_desc_blocks = %lu\n",
               fs->desc_blocks, new_desc_blocks);
-       if (!(fs->super->s_feature_compat &
-             EXT2_FEATURE_COMPAT_RESIZE_INODE) &&
-           new_desc_blocks != fs->desc_blocks) {
-               com_err(program_name, 0,
-                       _("Filesystem does not support online resizing"));
-               exit(1);
+
+       /*
+        * Do error checking to make sure the resize will be successful.
+        */
+       if ((access("/sys/fs/ext4/features/meta_bg_resize", R_OK) != 0) ||
+           getenv("RESIZE2FS_NO_META_BG_RESIZE")) {
+               if (!EXT2_HAS_COMPAT_FEATURE(fs->super,
+                                       EXT2_FEATURE_COMPAT_RESIZE_INODE) &&
+                   (new_desc_blocks != fs->desc_blocks)) {
+                       com_err(program_name, 0,
+                               _("Filesystem does not support online resizing"));
+                       exit(1);
+               }
+
+               if (EXT2_HAS_COMPAT_FEATURE(fs->super,
+                                       EXT2_FEATURE_COMPAT_RESIZE_INODE) &&
+                   new_desc_blocks > (fs->desc_blocks +
+                                      fs->super->s_reserved_gdt_blocks)) {
+                       com_err(program_name, 0,
+                               _("Not enough reserved gdt blocks for resizing"));
+                       exit(1);
+               }
+
+               if ((ext2fs_blocks_count(sb) > MAX_32_NUM) ||
+                   (*new_size > MAX_32_NUM)) {
+                       com_err(program_name, 0,
+                               _("Kernel does not support resizing a file system this large"));
+                       exit(1);
+               }
        }
 
        fd = open(mtpt, O_RDONLY);
@@ -101,13 +124,6 @@ errcode_t online_resize_fs(ext2_filsys fs, const char *mtpt,
                return 0;
        }
 
-       if ((ext2fs_blocks_count(sb) > MAX_32_NUM) ||
-           (*new_size > MAX_32_NUM)) {
-               com_err(program_name, 0,
-                       _("Kernel does not support resizing a file system "
-                         "this large"));
-               exit(1);
-       }
        size = ext2fs_blocks_count(sb);
 
        if (ioctl(fd, EXT2_IOC_GROUP_EXTEND, &size)) {