Re: [PATCH v3 3/6] xfs, dax: introduce IS_FSDAX()

[Jan Kara]

On Fri 23-02-18 16:43:27, Dan Williams wrote:
> Given that S_DAX is non-zero in the FS_DAX=n + DEV_DAX=y case, another
> mechanism besides the plain IS_DAX() check to compile out dead
> filesystem-dax code paths. Without IS_FSDAX() xfs will fail at link time
> with:
> 
>     ERROR: "dax_finish_sync_fault" [fs/xfs/xfs.ko] undefined!
>     ERROR: "dax_iomap_fault" [fs/xfs/xfs.ko] undefined!
>     ERROR: "dax_iomap_rw" [fs/xfs/xfs.ko] undefined!
> 
> This compile failure was previously hidden by the fact that S_DAX was
> erroneously defined to '0' in the FS_DAX=n + DEV_DAX=y case.
> 
> Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

As much as I appreciate that relying on compiler to optimize out dead
branches results in nicer looking code this is an example where it
backfires. Also having IS_DAX() and IS_FSDAX() doing almost the same, just
not exactly the same, is IMHO a recipe for confusion (e.g. a casual reader
could think why does ext4 get away with using IS_DAX while XFS has to use
IS_FSDAX?). So I'd just prefer to handle this as is usual in other kernel
areas - define empty stubs for all exported functions when CONFIG_FS_DAX is
not enabled. That way code can stay without ugly ifdefs and we don't have
to bother with IS_FSDAX vs IS_DAX distinction in filesystem code. Thoughts?

								Honza

> ---
>  fs/xfs/xfs_file.c    |   14 +++++++-------
>  fs/xfs/xfs_ioctl.c   |    4 ++--
>  fs/xfs/xfs_iomap.c   |    6 +++---
>  fs/xfs/xfs_reflink.c |    2 +-
>  include/linux/fs.h   |    2 ++
>  5 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 9ea08326f876..46a098b90fd0 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -288,7 +288,7 @@ xfs_file_read_iter(
>  	if (XFS_FORCED_SHUTDOWN(mp))
>  		return -EIO;
>  
> -	if (IS_DAX(inode))
> +	if (IS_FSDAX(inode))
>  		ret = xfs_file_dax_read(iocb, to);
>  	else if (iocb->ki_flags & IOCB_DIRECT)
>  		ret = xfs_file_dio_aio_read(iocb, to);
> @@ -726,7 +726,7 @@ xfs_file_write_iter(
>  	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
>  		return -EIO;
>  
> -	if (IS_DAX(inode))
> +	if (IS_FSDAX(inode))
>  		ret = xfs_file_dax_write(iocb, from);
>  	else if (iocb->ki_flags & IOCB_DIRECT) {
>  		/*
> @@ -1045,7 +1045,7 @@ __xfs_filemap_fault(
>  	}
>  
>  	xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> -	if (IS_DAX(inode)) {
> +	if (IS_FSDAX(inode)) {
>  		pfn_t pfn;
>  
>  		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &xfs_iomap_ops);
> @@ -1070,7 +1070,7 @@ xfs_filemap_fault(
>  {
>  	/* DAX can shortcut the normal fault path on write faults! */
>  	return __xfs_filemap_fault(vmf, PE_SIZE_PTE,
> -			IS_DAX(file_inode(vmf->vma->vm_file)) &&
> +			IS_FSDAX(file_inode(vmf->vma->vm_file)) &&
>  			(vmf->flags & FAULT_FLAG_WRITE));
>  }
>  
> @@ -1079,7 +1079,7 @@ xfs_filemap_huge_fault(
>  	struct vm_fault		*vmf,
>  	enum page_entry_size	pe_size)
>  {
> -	if (!IS_DAX(file_inode(vmf->vma->vm_file)))
> +	if (!IS_FSDAX(file_inode(vmf->vma->vm_file)))
>  		return VM_FAULT_FALLBACK;
>  
>  	/* DAX can shortcut the normal fault path on write faults! */
> @@ -1124,12 +1124,12 @@ xfs_file_mmap(
>  	 * We don't support synchronous mappings for non-DAX files. At least
>  	 * until someone comes with a sensible use case.
>  	 */
> -	if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
> +	if (!IS_FSDAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
>  		return -EOPNOTSUPP;
>  
>  	file_accessed(filp);
>  	vma->vm_ops = &xfs_file_vm_ops;
> -	if (IS_DAX(file_inode(filp)))
> +	if (IS_FSDAX(file_inode(filp)))
>  		vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
>  	return 0;
>  }
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 89fb1eb80aae..234279ff66ce 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1108,9 +1108,9 @@ xfs_ioctl_setattr_dax_invalidate(
>  	}
>  
>  	/* If the DAX state is not changing, we have nothing to do here. */
> -	if ((fa->fsx_xflags & FS_XFLAG_DAX) && IS_DAX(inode))
> +	if ((fa->fsx_xflags & FS_XFLAG_DAX) && IS_FSDAX(inode))
>  		return 0;
> -	if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_DAX(inode))
> +	if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_FSDAX(inode))
>  		return 0;
>  
>  	/* lock, flush and invalidate mapping in preparation for flag change */
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 66e1edbfb2b2..cf794d429aec 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -241,7 +241,7 @@ xfs_iomap_write_direct(
>  	 * the reserve block pool for bmbt block allocation if there is no space
>  	 * left but we need to do unwritten extent conversion.
>  	 */
> -	if (IS_DAX(VFS_I(ip))) {
> +	if (IS_FSDAX(VFS_I(ip))) {
>  		bmapi_flags = XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO;
>  		if (imap->br_state == XFS_EXT_UNWRITTEN) {
>  			tflags |= XFS_TRANS_RESERVE;
> @@ -952,7 +952,7 @@ static inline bool imap_needs_alloc(struct inode *inode,
>  	return !nimaps ||
>  		imap->br_startblock == HOLESTARTBLOCK ||
>  		imap->br_startblock == DELAYSTARTBLOCK ||
> -		(IS_DAX(inode) && imap->br_state == XFS_EXT_UNWRITTEN);
> +		(IS_FSDAX(inode) && imap->br_state == XFS_EXT_UNWRITTEN);
>  }
>  
>  static inline bool need_excl_ilock(struct xfs_inode *ip, unsigned flags)
> @@ -988,7 +988,7 @@ xfs_file_iomap_begin(
>  		return -EIO;
>  
>  	if (((flags & (IOMAP_WRITE | IOMAP_DIRECT)) == IOMAP_WRITE) &&
> -			!IS_DAX(inode) && !xfs_get_extsz_hint(ip)) {
> +			!IS_FSDAX(inode) && !xfs_get_extsz_hint(ip)) {
>  		/* Reserve delalloc blocks for regular writeback. */
>  		return xfs_file_iomap_begin_delay(inode, offset, length, iomap);
>  	}
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 270246943a06..a126e00e05e3 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1351,7 +1351,7 @@ xfs_reflink_remap_range(
>  		goto out_unlock;
>  
>  	/* Don't share DAX file data for now. */
> -	if (IS_DAX(inode_in) || IS_DAX(inode_out))
> +	if (IS_FSDAX(inode_in) || IS_FSDAX(inode_out))
>  		goto out_unlock;
>  
>  	ret = vfs_clone_file_prep_inodes(inode_in, pos_in, inode_out, pos_out,
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 79c413985305..a4310a95011b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1909,6 +1909,8 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
>  #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
>  				 (inode)->i_rdev == WHITEOUT_DEV)
>  
> +#define IS_FSDAX(inode) (IS_ENABLED(CONFIG_FS_DAX) && IS_DAX(inode))
> +
>  static inline bool HAS_UNMAPPED_ID(struct inode *inode)
>  {
>  	return !uid_valid(inode->i_uid) || !gid_valid(inode->i_gid);
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR