From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from li9-11.members.linode.com ([67.18.176.11]:49398 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754059Ab2FLTPb (ORCPT ); Tue, 12 Jun 2012 15:15:31 -0400 Date: Tue, 12 Jun 2012 15:15:27 -0400 From: "Ted Ts'o" To: kreijack@inwind.it Cc: linux-btrfs , Liu Bo Subject: Re: Btrfs and data nocow per inode basis Message-ID: <20120612191527.GA11966@thunk.org> References: <4FD442F1.7040008@inwind.it> <4FD77F45.3060000@libero.it> <20120612183209.GC1803@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120612183209.GC1803@thunk.org> Sender: linux-btrfs-owner@vger.kernel.org List-ID: It appears the NOCOW_FL flag is currently a no-op in the 3.2 kernel? {/mnt} 2062# grep /mnt /proc/mounts /dev/mapper/funarg-btrfs /mnt btrfs rw,relatime,space_cache 0 0 {/mnt} 2063# sync ; filefrag -v a Filesystem type is: 9123683e File size of a is 32768 (8 blocks, blocksize 4096) ext logical physical expected length flags 0 0 3096 8 eof a: 1 extent found {/mnt} 2064# dd if=/dev/zero of=a bs=32k conv=notrunc,nocreat count=1 1+0 records in 1+0 records out 32768 bytes (33 kB) copied, 0.000119266 s, 275 MB/s {/mnt} 2065# sync ; filefrag -v a Filesystem type is: 9123683e File size of a is 32768 (8 blocks, blocksize 4096) ext logical physical expected length flags 0 0 3088 8 eof a: 1 extent found {/mnt} 2066# lsattr a ---------------C a I've attached the patch which I was going to commit, but when I tested it, it appears the flag is being set and displayed correctly, but btrfs doesn't appear to be honoring it. Anyway want to explain what's going on? - Ted diff --git a/lib/e2p/pf.c b/lib/e2p/pf.c index f03193c..69181e7 100644 --- a/lib/e2p/pf.c +++ b/lib/e2p/pf.c @@ -49,6 +49,7 @@ static struct flags_name flags_array[] = { { EXT2_TOPDIR_FL, "T", "Top_of_Directory_Hierarchies" }, { EXT4_EXTENTS_FL, "e", "Extents" }, { EXT4_HUGE_FILE_FL, "h", "Huge_file" }, + { FS_NOCOW_FL, "C", "Huge_file" }, { 0, NULL, NULL } }; diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h index f46a1a9..fb3f7cc 100644 --- a/lib/ext2fs/ext2_fs.h +++ b/lib/ext2fs/ext2_fs.h @@ -301,6 +301,7 @@ struct ext2_dx_countlimit { #define EXT4_EXTENTS_FL 0x00080000 /* Inode uses extents */ #define EXT4_EA_INODE_FL 0x00200000 /* Inode used for large EA */ /* EXT4_EOFBLOCKS_FL 0x00400000 was here */ +#define FS_NOCOW_FL 0x00800000 /* Do not cow file */ #define EXT4_SNAPFILE_FL 0x01000000 /* Inode is a snapshot */ #define EXT4_SNAPFILE_DELETED_FL 0x04000000 /* Snapshot is being deleted */ #define EXT4_SNAPFILE_SHRUNK_FL 0x08000000 /* Snapshot shrink has completed */ diff --git a/misc/chattr.1.in b/misc/chattr.1.in index 92f6d70..18b44bd 100644 --- a/misc/chattr.1.in +++ b/misc/chattr.1.in @@ -64,6 +64,10 @@ this file compresses data before storing them on the disk. Note: please make sure to read the bugs and limitations section at the end of this document. .PP +A file with the 'C' attribute set will not be subject to copy-on-write +updates. This flag is only supported on file systems which perform +copy-on-write, obviously. +.PP When a directory with the `D' attribute set is modified, the changes are written synchronously on the disk; this is equivalent to the `dirsync' mount option applied to a subset of the files. diff --git a/misc/chattr.c b/misc/chattr.c index 8a2d61f..141ea6e 100644 --- a/misc/chattr.c +++ b/misc/chattr.c @@ -107,6 +107,7 @@ static const struct flags_char flags_array[] = { { EXT2_UNRM_FL, 'u' }, { EXT2_NOTAIL_FL, 't' }, { EXT2_TOPDIR_FL, 'T' }, + { FS_NOCOW_FL, 'C' }, { 0, 0 } };