From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:29938 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753428Ab2FLUoY (ORCPT ); Tue, 12 Jun 2012 16:44:24 -0400 Date: Tue, 12 Jun 2012 16:44:23 -0400 From: Chris Mason To: "Ted Ts'o" Cc: "kreijack@inwind.it" , linux-btrfs , Liu Bo Subject: Re: Btrfs and data nocow per inode basis Message-ID: <20120612204423.GA27777@shiny> References: <4FD442F1.7040008@inwind.it> <4FD77F45.3060000@libero.it> <20120612183209.GC1803@thunk.org> <20120612191527.GA11966@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120612191527.GA11966@thunk.org> Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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. -chris > > {/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 } > }; > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html