From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from li9-11.members.linode.com ([67.18.176.11]:49464 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752490Ab2FLVKt (ORCPT ); Tue, 12 Jun 2012 17:10:49 -0400 Date: Tue, 12 Jun 2012 17:10:44 -0400 From: "Ted Ts'o" To: Chris Mason , "kreijack@inwind.it" , linux-btrfs , Liu Bo Subject: Re: Btrfs and data nocow per inode basis Message-ID: <20120612211043.GH12161@thunk.org> References: <4FD442F1.7040008@inwind.it> <4FD77F45.3060000@libero.it> <20120612183209.GC1803@thunk.org> <20120612191527.GA11966@thunk.org> <20120612204423.GA27777@shiny> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120612204423.GA27777@shiny> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Jun 12, 2012 at 04:44:23PM -0400, Chris Mason wrote: > On Tue, Jun 12, 2012 at 01:15:27PM -0600, Ted Ts'o wrote: > > It appears the NOCOW_FL flag is currently a no-op in the 3.2 kernel? > > It's not a noop, but it is only setting the NODATACOW flag. It needs to > set the nodatasum flag as well, just like the mount -o nodatacow mount > option does. > > I'll fix this up on the kernel side, thanks Ted. Here's the final patch to e2fsprogs that will be going into 1.42.4: commit 5a23c93aeb65d61892a47f8f27bffad38f4759ea Author: Theodore Ts'o Date: Tue Jun 12 17:09:39 2012 -0400 lsattr, chattr: add support for btrfs's No_COW flag Signed-off-by: "Theodore Ts'o" diff --git a/lib/e2p/pf.c b/lib/e2p/pf.c index f03193c..e2f8ce5 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", "No_COW" }, { 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..5a57d2c 100644 --- a/misc/chattr.1.in +++ b/misc/chattr.1.in @@ -64,6 +64,15 @@ 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. (Note: For btrfs, the 'C' flag should be only +set on new or empty files. If it is set on a file which already has +data blocks, it is undefined when the blocks assigned to the file will +be fully stable. If the 'C' flag is set on a directory, it will have no +effect on the directory, but new files created in that directory will +the No_COW attribute.) +.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. @@ -159,8 +168,7 @@ maintained by Theodore Ts'o . .SH BUGS AND LIMITATIONS The `c', 's', and `u' attributes are not honored by the ext2 and ext3 filesystems as implemented in the current mainline -Linux kernels. These attributes may be implemented -in future versions of the ext2 and ext3 filesystems. +Linux kernels. .PP The `j' option is only useful if the filesystem is mounted as ext3. .PP 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 } };