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Message-ID: <5F32BA3E.90801@cn.fujitsu.com>
Date:   Tue, 11 Aug 2020 23:33:18 +0800
From:   Xiao Yang <yangx.jy@cn.fujitsu.com>
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To:     Ira Weiny <ira.weiny@intel.com>
CC:     <darrick.wong@oracle.com>, <tytso@mit.edu>, <ebiggers@kernel.org>,
        <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH v2] chattr/lsattr: Support dax attribute
References: <20200728053321.12892-1-yangx.jy@cn.fujitsu.com> <20200807160305.GQ1573827@iweiny-DESK2.sc.intel.com>
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On 2020/8/8 0:03, Ira Weiny 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?
Hi Ira,

Thanks for your reply. :-)
chattr failed to set the 'x' flag on ext2 sliently because ext2_ioctl() 
in kernel drops
unsupported 'FS_DAX_FL' sliently:
----------------------------------------------
# touch file
# chattr +x file;echo $?
0
# lsattr file
--------------------- file
----------------------------------------------

ext2_ioctl() drops all unsupported flags sliently(see the following 
code) so I am
not sure if we should return -EOPNOTSUPP for the unsupported  FS_DAX_FL:
----------------------------------------------
long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
...
         case EXT2_IOC_SETFLAGS: {
...
                 flags = flags & EXT2_FL_USER_MODIFIABLE;
                 flags |= oldflags & ~EXT2_FL_USER_MODIFIABLE;
                 ei->i_flags = flags;

                 ext2_set_inode_flags(inode);
...
----------------------------------------------

Best Regards,
Xiao Yang
> Ira
>
>>   #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
>>
>>
>>
>
> .
>