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@xxxxxxxxxxxxxx>
> ---
> 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.
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.
--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
>
>
>
