Re: [PATCH 2/2] E2fsprogs: add compress and cow support in chattr, lsattr

[Lutz Vieweg <lvml@5t9.de>]

On 04/18/2011 09:37 AM, liubo wrote:
> Modify command 'chattr' and 'lsattr' to support compress and cow.
> - use 'C' to indicate NOCOW attribute.

It's kind of confusing for new users that when one sets
 > chattr +C someexistingfile
on btrfs, a subsequent
 > lsattr someexistingfile
will show the C flag as "not set". It takes some
reading to realize that btrfs cannot change the non-COW
flag on files bigger than 0 bytes.

Maybe "chattr +C" could print a warning if a file
to change attributes for is > 0 bytes long?

Regards,

Lutz Vieweg


> Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
> ---
>   lib/e2p/pf.c         |    1 +
>   lib/ext2fs/ext2_fs.h |    1 +
>   misc/chattr.1.in     |   15 +++++++++++----
>   misc/chattr.c        |   15 ++++++++++++++-
>   4 files changed, 27 insertions(+), 5 deletions(-)
>
> diff --git a/lib/e2p/pf.c b/lib/e2p/pf.c
> index cc50896..c9385dd 100644
> --- a/lib/e2p/pf.c
> +++ b/lib/e2p/pf.c
> @@ -48,6 +48,7 @@ static struct flags_name flags_array[] = {
>   	{ FS_TOPDIR_FL, "T", "Top_of_Directory_Hierarchies" },
>   	{ EXT4_EXTENTS_FL, "e", "Extents" },
>   	{ EXT4_HUGE_FILE_FL, "h", "Huge_file" },
> +	{ FS_NOCOW_FL, "C", "NOCOW" },
>   	{ 0, NULL, NULL }
>   };
>
> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
> index 858c103..776be92 100644
> --- a/lib/ext2fs/ext2_fs.h
> +++ b/lib/ext2fs/ext2_fs.h
> @@ -276,6 +276,7 @@ struct ext2_dx_countlimit {
>   #define EXT4_EXTENTS_FL 		0x00080000 /* Inode uses extents */
>   #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
>   #define EXT4_EOFBLOCKS_FL		0x00400000 /* Blocks allocated beyond EOF */
> +#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..434eb04 100644
> --- a/misc/chattr.1.in
> +++ b/misc/chattr.1.in
> @@ -19,17 +19,18 @@ chattr \- change file attributes on a Linux file system
>   .B chattr
>   changes the file attributes on a Linux file system.
>   .PP
> -The format of a symbolic mode is +-=[acdeijstuADST].
> +The format of a symbolic mode is +-=[acdeijstuACDST].
>   .PP
>   The operator `+' causes the selected attributes to be added to the
>   existing attributes of the files; `-' causes them to be removed; and
>   `=' causes them to be the only attributes that the files have.
>   .PP
> -The letters `acdeijstuADST' select the new attributes for the files:
> +The letters `acdeijstuACDST' select the new attributes for the files:
>   append only (a), compressed (c), no dump (d), extent format (e), immutable (i),
>   data journalling (j), secure deletion (s), no tail-merging (t),
> -undeletable (u), no atime updates (A), synchronous directory updates (D),
> -synchronous updates (S), and top of directory hierarchy (T).
> +undeletable (u), no atime updates (A), no copy on write (C),
> +synchronous directory updates (D), synchronous updates (S),
> +and top of directory hierarchy (T).
>   .PP
>   The following attributes are read-only, and may be listed by
>   .BR lsattr (1)
> @@ -64,6 +65,10 @@ 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 is marked without COW (copy on write).  Note:
> +please make sure to read the bugs and limitations section at the end of this
> +document.
> +.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.
> @@ -161,6 +166,8 @@ 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.
> +The `C' attribute is only used in btrfs filesystem in the current mainline
> +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 78e3736..8c8231e 100644
> --- a/misc/chattr.c
> +++ b/misc/chattr.c
> @@ -82,7 +82,7 @@ static unsigned long sf;
>   static void usage(void)
>   {
>   	fprintf(stderr,
> -		_("Usage: %s [-RVf] [-+=AacDdeijsSu] [-v version] files...\n"),
> +		_("Usage: %s [-RVf] [-+=AacDdeijsSuC] [-v version] files...\n"),
>   		program_name);
>   	exit(1);
>   }
> @@ -106,6 +106,7 @@ static const struct flags_char flags_array[] = {
>   	{ FS_UNRM_FL, 'u' },
>   	{ FS_NOTAIL_FL, 't' },
>   	{ FS_TOPDIR_FL, 'T' },
> +	{ FS_NOCOW_FL, 'C' },
>   	{ 0, 0 }
>   };
>
> @@ -159,6 +160,12 @@ static int decode_arg (int * i, int argc, char ** argv)
>   			}
>   			if ((fl = get_flag(*p)) == 0)
>   				usage();
> +
> +			if (fl == FS_COMPR_FL) {
> +				af |= FS_NOCOMPR_FL;
> +				add = 1;
> +			}
> +
>   			rf |= fl;
>   			rem = 1;
>   		}
> @@ -168,6 +175,12 @@ static int decode_arg (int * i, int argc, char ** argv)
>   		for (p = &argv[*i][1]; *p; p++) {
>   			if ((fl = get_flag(*p)) == 0)
>   				usage();
> +
> +			if (fl == FS_COMPR_FL) {
> +				rf |= FS_NOCOMPR_FL;
> +				rem = 1;
> +			}
> +
>   			af |= fl;
>   		}
>   		break;
>