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

[Xiao Yang <yangx.jy@xxxxxxxxxxxxxx>]

On 2020/8/13 7:25, Andreas Dilger wrote:
> On Aug 7, 2020, at 10:03 AM, Ira Weiny<ira.weiny@xxxxxxxxx>  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@xxxxxxxxxxxxxx>
> > > ---
> > >
> > > 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