On Fri 03-04-20 11:18:43, Ira Weiny wrote: > Ok For 5.8 why don't we not allow FS_XFLAG_DAX to be changed on files _at_ > _all_... > > 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... OK, after considering all the options we were hashing out here, I think this is the best API. There isn't the confusing "S_DAX will magically switch on inode eviction" and although the functionality is limited, I think 90% of users would end up using the functionality like this anyway. > - 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. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
