On Tue, Oct 31, 2017 at 07:21:59PM +0000, Nick Terrell wrote: > On 10/31/17, 9:48 AM, "David Sterba" <dste...@suse.com> wrote: > > The current default for the compression file flag is 'zlib', the zstd > > patch silently changed that to zstd. Though the choice of zlib might not > > be the best one, we should keep the backward compatibility. > > Sorry about that, I didn't intentionally change it. I checked over my patch, > and the only other place where an "else" was changed is the other place in > ioctl.c, which looks okay to me. > > I'm trying to expose the buggy case in 4.14-rc7. However, since > fs_info->compress_type defaults to ZLIB when -compress is not passed, and > when -compress=no is passed, fs_info->compress_type is not modified, I > don't know how to get fs_info->compress_type to be BTRFS_COMPRESS_NONE. > Is there a way that fs_info->compress_type can be BTRFS_COMPRESS_NONE?
And it turns out that this is not possible, fs_info::compress_type will always be one of lzo/zlib/zstd. This is zlib by default, so any chattr +c will set zlib. In order to set zstd by chattr, there would have to be at least one mount with zstd or defrag -czstd. And this will set the incompat bit. > I modified -compress=no to set fs_info->compress_type=BTRFS_COMPRESS_NONE > and the ioctl() call set the compression type to zstd before your patch, > and zlib after, as expected. I must have assumed that mounting with -o compress=no will reset the compress_type. So unless I missed something else, the default will not change and the feature flags match the actual filesystem state. False alert, sorry. At least I don't have to send a late pull request. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
