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Date:   Thu, 24 Jun 2021 10:23:29 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>
Subject: Re: [PATCH 2/2] fs: ext4: Add check to prevent attempting to resize
 an fs with sparse_super2

On Mon, Jun 07, 2021 at 12:15:24PM -0700, Josh Triplett wrote:
> The in-kernel ext4 resize code doesn't support filesystem with the
> sparse_super2 feature. It fails with errors like this and doesn't finish
> the resize:
> EXT4-fs (loop0): resizing filesystem from 16640 to 7864320 blocks
> EXT4-fs warning (device loop0): verify_reserved_gdb:760: reserved GDT 2 missing grp 1 (32770)
> EXT4-fs warning (device loop0): ext4_resize_fs:2111: error (-22) occurred during file system resize
> EXT4-fs (loop0): resized filesystem to 2097152
> 
> To reproduce:
> mkfs.ext4 -b 4096 -I 256 -J size=32 -E resize=$((256*1024*1024)) -O sparse_super2 ext4.img 65M
> truncate -s 30G ext4.img
> mount ext4.img /mnt
> python3 -c 'import fcntl, os, struct ; fd = os.open("/mnt", os.O_RDONLY | os.O_DIRECTORY) ; fcntl.ioctl(fd, 0x40086610, struct.pack("Q", 30 * 1024 * 1024 * 1024 // 4096), False) ; os.close(fd)'
> dmesg | tail
> e2fsck ext4.img
> 
> The userspace resize2fs tool has a check for this case: it checks if the
> filesystem has sparse_super2 set and if the kernel provides
> /sys/fs/ext4/features/sparse_super2. However, the former check requires
> manually reading and parsing the filesystem superblock.
> 
> Detect this case in ext4_resize_begin and error out early with a clear
> error message.
> 
> Signed-off-by: Josh Triplett <josh@...htriplett.org>

Applied, thanks.

					- Ted

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