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Message-Id: <3CAF5E28-8718-4078-ACB9-607CA8DC5BA5@dilger.ca> Date: Mon, 29 Apr 2013 12:35:18 -0600 From: Andreas Dilger <adilger@...ger.ca> To: Lukáš Czerner <lczerner@...hat.com> Cc: "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org> Subject: Re: [PATCH] ext4: Reserve FEATURE_RO_COMPAT and INO flag On 2013-04-29, at 6:58 AM, Lukáš Czerner wrote: > On Fri, 26 Apr 2013, Andreas Dilger wrote: >> Date: Fri, 26 Apr 2013 05:47:58 -0600 >> From: Andreas Dilger <adilger@...ger.ca> >> To: Lukas Czerner <lczerner@...hat.com> >> Cc: "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>, >> Lukas Czerner <lczerner@...hat.com> >> Subject: Re: [PATCH] ext4: Reserve FEATURE_RO_COMPAT and INO flag >> >> I was looking in the maint and master branches, but I don't see these flags anywhere? > > That's odd. I am using git repository: > > git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git > > and it is there added with the commit > 991211f676f49c6cf30af368dade2f81287f1fa8 libext2fs, libe2p: Reserve > RO_COMPAT_REPLICA feature Strange, I see it now. I don't know what file I was looking at that didn't have this included... One real problem that I see is that EXT4_REPLICA_INO uses the last reserved inode. I recall in the past that Ted wanted to make this last reserved inode a hidden directory, so that it would be possible to put special inodes in there and access them by name. Not quite as easy as accessing a reserved inode by number, but still preferable to not being able to have filesystem internal inodes at all in the future. Of the currently-reserved inodes, the only other one that might be a potential candidate for re-use is EXT2_UNDEL_DIR_INO, which has never been used in any upstream kernel (Googling shows there was a patch developed by some students, but never released AFAICS). The BOOT_LOADED_INO has recently seen interest for use by Grub, and real patches exist for the snapshot code . That leaves us in a quandry - change the meaning of a reserved inode which has been publicly available for many years but never really used, or change the meaning of a private reserved inode which is (presumably) in use privately, but will (presumably) never be landed? IMHO, since EXT2_UNDEL_DIR_INO was already supposed to be a directory it might be reasonable to repurpose it to be an "internal files" directory, possibly even linking the existing reserved directories to it by name for consistency? This concept is used by ZFS to store all kinds of configuration data, mount parameters and tunables, etc. and is very handy IMHO. Cheers, Andreas >> On 2013-04-25, at 8:39, Lukas Czerner <lczerner@...hat.com> wrote: >> >>> EXT4_FEATURE_RO_COMPAT_REPLICA and EXT4_REPLICA_INO are reserved in >>> e2fsprogs for non-upstream feature. However it has never been reserved >>> in kernel, fix this. Thanks to Radek Pazdera to pointing it out. >>> >>> Signed-off-by: Lukas Czerner <lczerner@...hat.com> >>> --- >>> fs/ext4/ext4.h | 3 +++ >>> 1 files changed, 3 insertions(+), 0 deletions(-) >>> >>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h >>> index 3b83cd6..6369c28 100644 >>> --- a/fs/ext4/ext4.h >>> +++ b/fs/ext4/ext4.h >>> @@ -241,6 +241,7 @@ struct ext4_io_submit { >>> #define EXT4_UNDEL_DIR_INO 6 /* Undelete directory inode */ >>> #define EXT4_RESIZE_INO 7 /* Reserved group descriptors inode */ >>> #define EXT4_JOURNAL_INO 8 /* Journal inode */ >>> +#define EXT4_REPLICA_INO 10 /* Used by non-upstream feature */ >>> >>> /* First non-reserved inode for old ext4 filesystems */ >>> #define EXT4_GOOD_OLD_FIRST_INO 11 >>> @@ -1481,6 +1482,8 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei) >>> * GDT_CSUM bits are mutually exclusive. >>> */ >>> #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM 0x0400 >>> +/* Reserved for non-upstream feature */ >>> +#define EXT4_FEATURE_RO_COMPAT_REPLICA 0x0800 >>> >>> #define EXT4_FEATURE_INCOMPAT_COMPRESSION 0x0001 >>> #define EXT4_FEATURE_INCOMPAT_FILETYPE 0x0002 >>> -- >>> 1.7.7.6 >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >>> the body of a message to majordomo@...r.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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