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Date: Mon, 21 Sep 2020 10:15:28 +0800
From: Xiao Yang <yangx.jy@...fujitsu.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
"tytso@....edu" <tytso@....edu>,
"ebiggers@...nel.org" <ebiggers@...nel.org>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] chattr/lsattr: Support dax attribute
On 2020/9/18 8:52, Ira Weiny wrote:
> On Mon, Jul 27, 2020 at 10:33:21PM -0700, Xiao Yang wrote:
>> Use the letter 'x' to set/get dax attribute on a directory/file.
> This may allow the flag to be set but I don't think this implements the logic
> within ext2 to properly support the flag does it?
Hi Ira,
In ext2, the dax flag cannot be set because ext2_ioctl() uses
EXT2_FL_USER_MODIFIABLE to drop
the unsupported flag.
> Just a quick look shows that ext2_ioctl() does not have any dax checks in it
> and you don't add them here?
The dax flag never be passed into ext2 actually so I don't think we need
some dax checks.
> So how does this work? Does ext2 share all the code with ext4 to make it work?
1) ext2 without CONFIG_EXT4_USE_FOR_EXT2 unsupports the dax flag and
ignores it sliently.
2) ext2 with CONFIG_EXT4_USE_FOR_EXT2 supports the dax flag.
Thanks,
Xiao Yang
> Ira
>
>> Signed-off-by: Xiao Yang<yangx.jy@...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 */
>> #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
>>
>>
>>
>
> .
>
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