On Thu, Jan 07, 2021 at 08:54:29PM -0600, Eric Sandeen wrote: > On 1/7/21 7:29 PM, Darrick J. Wong wrote: > > On Thu, Jan 07, 2021 at 03:36:34PM -0600, Eric Sandeen wrote: > >> Today, xfs_reflink_remap_prep() will reject inodes which are in the CPU > >> direct access state, i.e. IS_DAX() is true. However, it is possible to > >> have inodes with the XFS_DIFLAG2_DAX set, but which are not activated as > >> dax, due to the flag being set after the inode was loaded. > >> > >> To avoid confusion and make the lack of dax+reflink crystal clear for the > >> user, reject reflink requests for both IS_DAX and XFS_DIFLAG2_DAX inodes > >> unless DAX mode is impossible due to mounting with -o dax=never. > > > > I thought we were allowing arbitrary combinations of DAX & REFLINK inode > > flags now, since we're now officially ok with "you set the inode flag > > but you don't get cpu direct access because $reasons"? > > *shrug* I think "haha depending on the order and the state we may or may > not let you reflink files with the dax flag set on disk so good luck" is > pretty confusing, and I figured this made things more obvious. > > I thought that should be an absolute, hch thought it should be ignored > for dax=never, and now ... ? > > I think the the current behavior is a bad user experience violating= > principle of least surprise, but I guess we don't have agreement on that. I guess not...? :( In /me's head, S_DAX is a best-effort affair -- if the storage supports it, and the cpu supports it, and the fs supports it, and the sysadmin didn't forbid it, and there's no file state preventing it, *then* you actually get S_DAX. DIFLAG2_DAX is merely advisory, so it's perfectly valid for reflink to come along and add a file state that (on this kernel) prevents DIFLAG2_DAX from causing S_DAX to get set. (We've probably already gone around and around on this elsewhere, but I'm catching up on 6 weeks of email...) > -Eric > > > --D > > > >> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> > >> --- > >> V2: Allow reflinking dax-flagged inodes in "mount -o dax=never" mode > >> > >> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > >> index 6fa05fb78189..e238a5b7b722 100644 > >> --- a/fs/xfs/xfs_reflink.c > >> +++ b/fs/xfs/xfs_reflink.c > >> @@ -1308,6 +1308,15 @@ xfs_reflink_remap_prep( > >> if (IS_DAX(inode_in) || IS_DAX(inode_out)) > >> goto out_unlock; > >> > >> + /* > >> + * Until we have dax+reflink, don't allow reflinking dax-flagged > >> + * inodes unless we are in dax=never mode. > >> + */ > >> + if (!(mp->m_flags & XFS_MOUNT_DAX_NEVER) && > >> + (src->i_d.di_flags2 & XFS_DIFLAG2_DAX || > >> + dest->i_d.di_flags2 & XFS_DIFLAG2_DAX)) I think the bitflag tests need parentheses around them, right? --D > >> + goto out_unlock; > >> + > >> ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out, > >> len, remap_flags); > >> if (ret || *len == 0) > >> > >
