Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5

Ira Weiny
2020-04-03T18:21:25Z

On Fri, Apr 03, 2020 at 11:18:43AM -0700, 'Ira Weiny' wrote:
[snip]

>
> Ok For 5.8 why don't we not allow FS_XFLAG_DAX to be changed on files _at_
> _all_...

To be fair, I believe Christoph advocated for this at one time or another...

Ira

>
> In summary:
>
> - Applications must call statx to discover the current S_DAX state.
>
> - There exists an advisory file inode flag FS_XFLAG_DAX that is set based on
> the parent directory FS_XFLAG_DAX inode flag. (There is no way to change
> this flag after file creation.)
>
> If FS_XFLAG_DAX is set and the fs is on pmem then it will enable S_DAX at
> inode load time; if FS_XFLAG_DAX is not set, it will not enable S_DAX.
> Unless overridden...
>
> - There exists a dax= mount option.
>
> "-o dax=off" means "never set S_DAX, ignore FS_XFLAG_DAX"
> "-o nodax" means "dax=off"
> "-o dax=always" means "always set S_DAX (at least on pmem), ignore FS_XFLAG_DAX"
> "-o dax" by itself means "dax=always"
> "-o dax=iflag" means "follow FS_XFLAG_DAX" and is the default
>
> - There exists an advisory directory inode flag FS_XFLAG_DAX that can be
> changed at any time. The flag state is copied into any files or
> subdirectories when they are created within that directory. If programs
> require file access runs in S_DAX mode, they'll have to create those files
> inside a directory with FS_XFLAG_DAX set, or mount the fs with an
> appropriate dax mount option.
>
>
> ???
>
> Ira
>