linux-ext4 - Re: [PATCH] chattr/lsattr: Support dax attribute

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Date:   Tue, 28 Jul 2020 09:12:40 +0800
From:   Xiao Yang <yangx.jy@...fujitsu.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
CC:     <ira.weiny@...el.com>, <tytso@....edu>,
        <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] chattr/lsattr: Support dax attribute

Hi Darrick,

Thanks for your review.

On 2020/7/28 0:08, Darrick J. Wong wrote:
> On Mon, Jul 27, 2020 at 05:29:01PM +0800, Xiao Yang wrote:
>> Use the letter 'x' to set/get dax attribute on a directory/file.
>>
>> Signed-off-by: Xiao Yang<yangx.jy@...fujitsu.com>
>> ---
>>   lib/e2p/pf.c         |  1 +
>>   lib/ext2fs/ext2_fs.h |  1 +
>>   misc/chattr.1.in     | 10 ++++++++--
>>   misc/chattr.c        |  3 ++-
>>   4 files changed, 12 insertions(+), 3 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..b5e2e42a 100644
>> --- a/lib/ext2fs/ext2_fs.h
>> +++ b/lib/ext2fs/ext2_fs.h
>> @@ -334,6 +334,7 @@ struct ext2_dx_tail {
>>   #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 FS_DAX_FL			0x02000000 /* Inode is DAX */
>>   #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 ff2fcf00..b27c8e1f 100644
>> --- a/misc/chattr.1.in
>> +++ b/misc/chattr.1.in
>> @@ -23,7 +23,7 @@ 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 '='
>> @@ -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 +211,11 @@ 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
>> +A file with the 'x' attribute set is accessed directly on the memory-like
>> +disk(e.g. /dev/pmem) by the kernel.  Kernel will skip page cache and do
>> +reads/writes on the file directly.
> There's much more to FS_DAX_FL than that.

Agreed.   Sorry for the rough description.

> See the "Enabling DAX on XFS and ext4" section of
> Documentation/filesystems/dax.txt.
>
> Note the part where you can set it on directories too; and also the part
> where there's a separate state for whether or not you get the pagecache
> bypass.

I will try to add more detailed description in v2 patch.

Thanks,
Xiao Yang
> --D
>
>> +.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
>>
>>
>>
>
> .
>