Re: [PATCH v2] chattr/lsattr: Support dax attribute

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2020/8/13 7:25, Andreas Dilger wrote:
> On Aug 7, 2020, at 10:03 AM, Ira Weiny<ira.weiny@intel.com>  wrote:
>> On Tue, Jul 28, 2020 at 01:33:21PM +0800, Xiao Yang wrote:
>>> Use the letter 'x' to set/get dax attribute on a directory/file.
>>>
>>> Signed-off-by: Xiao Yang<yangx.jy@cn.fujitsu.com>
>>> ---
>>>
>>> V1->V2:
>>> 1) Define FS_DAX_FL in order and add missing 'x' letter in manpage.
>>> 2) Add more detailed description about 'x' attribute.
>>> 3) 'x' is a separate attribute and doesn't always affect S_DAX(i.e.
>>>    pagecache bypass) so remove the related info.
>>>
>>> lib/e2p/pf.c         |  1 +
>>> lib/ext2fs/ext2_fs.h |  1 +
>>> misc/chattr.1.in     | 15 ++++++++++++---
>>> misc/chattr.c        |  3 ++-
>>> 4 files changed, 16 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/lib/e2p/pf.c b/lib/e2p/pf.c
>>> index 0c6998c4..e59cccff 100644
>>> --- a/lib/e2p/pf.c
>>> +++ b/lib/e2p/pf.c
>>> @@ -44,6 +44,7 @@ static struct flags_name flags_array[] = {
>>> 	{ EXT2_TOPDIR_FL, "T", "Top_of_Directory_Hierarchies" },
>>> 	{ EXT4_EXTENTS_FL, "e", "Extents" },
>>> 	{ FS_NOCOW_FL, "C", "No_COW" },
>>> +	{ FS_DAX_FL, "x", "Dax" },
>>> 	{ EXT4_CASEFOLD_FL, "F", "Casefold" },
>>> 	{ EXT4_INLINE_DATA_FL, "N", "Inline_Data" },
>>> 	{ EXT4_PROJINHERIT_FL, "P", "Project_Hierarchy" },
>>> diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
>>> index 6c20ea77..88f510a3 100644
>>> --- a/lib/ext2fs/ext2_fs.h
>>> +++ b/lib/ext2fs/ext2_fs.h
>>> @@ -335,6 +335,7 @@ struct ext2_dx_tail {
>>> /* 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 FS_DAX_FL			0x02000000 /* Inode is DAX */
>> Per-file support is not supported on ext2...
>>
>> So I'm suspicious of this change.  It is probably not an issue but I just
>> wanted to check if you are trying to test on ext2?
> It is up to the kernel to handle the various flags, definitely the chattr
> command should not be trying to guess which flags are supported, since
> this can definitely change between kernels and the underlying filesystems.
Hi Andreas,

Agreed,  the various flags are handled by kernel instead of chattr 
command. :-)

Best Regards,
Xiao Yang
> Note that the headers in e2fsprogs are all using "ext2" in the name,
> regardless of the fact that the flags apply to ext3 and ext4.
>
> Cheers, Andreas
>
>>> #define EXT4_SNAPFILE_DELETED_FL	0x04000000  /* Snapshot is being deleted */
>>> #define EXT4_SNAPFILE_SHRUNK_FL		0x08000000  /* Snapshot shrink has completed */
>>> #define EXT4_INLINE_DATA_FL		0x10000000 /* Inode has inline data */
>>> diff --git a/misc/chattr.1.in b/misc/chattr.1.in
>>> index ff2fcf00..5a4928a5 100644
>>> --- a/misc/chattr.1.in
>>> +++ b/misc/chattr.1.in
>>> @@ -23,13 +23,13 @@ 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 +-=[aAcCdDeFijPsStTu].
>>> +The format of a symbolic mode is +-=[aAcCdDeFijPsStTux].
>>> .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 'aAcCdDeFijPsStTu' select the new attributes for the files:
>>> +The letters 'aAcCdDeFijPsStTux' select the new attributes for the files:
>>> append only (a),
>>> no atime updates (A),
>>> compressed (c),
>>> @@ -45,7 +45,8 @@ secure deletion (s),
>>> synchronous updates (S),
>>> no tail-merging (t),
>>> top of directory hierarchy (T),
>>> -and undeletable (u).
>>> +undeletable (u),
>>> +and direct access for files (x).
>>> .PP
>>> The following attributes are read-only, and may be listed by
>>> .BR lsattr (1)
>>> @@ -210,6 +211,14 @@ saved.  This allows the user to ask for its undeletion.  Note: please
>>> make sure to read the bugs and limitations section at the end of this
>>> document.
>>> .TP
>>> +.B x
>>> +The 'x' attribute can be set on a directory or file.  If the attribute
>>> +is set on an existing directory, it will be inherited by all files and
>>> +subdirectories that are subsequently created in the directory.  If an
>>> +existing directory has contained some files and subdirectories, modifying
>>> +the attribute on the parent directory doesn't change the attributes on
>>> +these files and subdirectories.
>>> +.TP
>>> .B V
>>> A file with the 'V' attribute set has fs-verity enabled.  It cannot be
>>> written to, and the filesystem will automatically verify all data read
>>> diff --git a/misc/chattr.c b/misc/chattr.c
>>> index a5d60170..c0337f86 100644
>>> --- a/misc/chattr.c
>>> +++ b/misc/chattr.c
>>> @@ -86,7 +86,7 @@ static unsigned long sf;
>>> static void usage(void)
>>> {
>>> 	fprintf(stderr,
>>> -		_("Usage: %s [-pRVf] [-+=aAcCdDeijPsStTuF] [-v version] files...\n"),
>>> +		_("Usage: %s [-pRVf] [-+=aAcCdDeijPsStTuFx] [-v version] files...\n"),
>>> 		program_name);
>>> 	exit(1);
>>> }
>>> @@ -112,6 +112,7 @@ static const struct flags_char flags_array[] = {
>>> 	{ EXT2_NOTAIL_FL, 't' },
>>> 	{ EXT2_TOPDIR_FL, 'T' },
>>> 	{ FS_NOCOW_FL, 'C' },
>>> +	{ FS_DAX_FL, 'x' },
>>> 	{ EXT4_CASEFOLD_FL, 'F' },
>>> 	{ 0, 0 }
>>> };
>>> --
>>> 2.21.0
>>>
>>>
>>>
>
> Cheers, Andreas
>
>
>
>
>