From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cantor2.suse.de ([195.135.220.15]:32923 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752794AbaF0PaU (ORCPT ); Fri, 27 Jun 2014 11:30:20 -0400 Date: Fri, 27 Jun 2014 17:30:18 +0200 From: David Sterba To: Eric Sandeen Cc: linux-btrfs Subject: Re: [PATCH] btrfs-progs: add supported attr flags to btrfs(5) Message-ID: <20140627153017.GF1553@suse.cz> Reply-To: dsterba@suse.cz References: <53AC84C9.2080106@redhat.com> <20140627134257.GE1553@twin.jikos.cz> <53AD860A.8090804@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <53AD860A.8090804@redhat.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Fri, Jun 27, 2014 at 09:56:10AM -0500, Eric Sandeen wrote: > > * and 'X' does not mean "no compression" and never has, although I'd > > like to see a chattr bit for that because we have the corresponding > > inode bit > > Ok, then I'm not sure what it does mean. Supposedly these flags are supported; > via check_flags(), called by setflags(), which I was basing these on: > > if (flags & ~(FS_IMMUTABLE_FL | FS_APPEND_FL | \ > FS_NOATIME_FL | FS_NODUMP_FL | \ > FS_SYNC_FL | FS_DIRSYNC_FL | \ > FS_NOCOMP_FL | FS_COMPR_FL | > FS_NOCOW_FL)) > > and the kernel header says that's: > > #define FS_NOCOMP_FL 0x00000400 /* Don't compress */ Passing this bit directly via ioctl works as expected, but to my knowledge there is no chattr letter allocated for it. > chattr(1) says: "compression raw access (X)," and also "The ’X’ attribute > is used by the experimental compression patches to indicate that a raw > contents of a compressed file can be accessed directly. It currently > may not be set or reset using chattr(1), although it can be displayed by lsattr(1)." > > Hum, ok, so we are starting to go off the rails here, aren't we ;) Yeah. And there's no support for accessing raw compressed data. > e2fsprogs has this flag translation: > { EXT2_NOCOMPR_FL, "X", "Compression_Raw_Access" }, > for: > #define EXT2_NOCOMPR_FL 0x00000400 /* Access raw compressed data */ > > and btrfs_ioctl_setflags claims to handle it: > > if (flags & FS_NOCOMP_FL) { > ip->flags &= ~BTRFS_INODE_COMPRESS; > ip->flags |= BTRFS_INODE_NOCOMPRESS; > ... > > so hopefully you can understand my confusion? ;) Oh I do now, but it's ext2 fault :) > The comment says: > > * The COMPRESS flag can only be changed by users, while the NOCOMPRESS > * flag may be changed automatically if compression code won't make > * things smaller. > > (but doesn't says "may *only* be...") And thats IMO right (at least I expect it work like that), the user may set or drop the NOCOMPRESS flag. The comment says that it may appear without user interaction. > But OTOH, chattr won't ever even *pass* "X" to the fs, will it. > > So I guess I'm lost. It looks like there's code to handle an incoming > "X" but I don't think chattr will send it. > > Do we ever get an outbound "X" for an opportunistically not-compressed file? > If so, maybe that still needs to be specified. AFAICS 'X' is not listed among the standard chattr options and chattr.c in e2fsprogs has no support for that. There is lib/e2p/pf.c: { EXT2_NOCOMPR_FL, "X", "Compression_Raw_Access" }, but this is used only locally by print_flags. I hope this answers your questions, 'X' has no meaning for btrfs now.