Re: [PATCH 12/18] btrfs: allow MAP_SYNC mmap

[Adam Borowski <kilobyte@angband.pl>]

On Thu, May 23, 2019 at 03:44:49PM +0200, Jan Kara wrote:
> On Mon 29-04-19 12:26:43, Goldwyn Rodrigues wrote:
> > From: Adam Borowski <kilobyte@angband.pl>
> > 
> > Used by userspace to detect DAX.
> > [rgoldwyn@suse.com: Added CONFIG_FS_DAX around mmap_supported_flags]
> 
> Why the CONFIG_FS_DAX bit? Your mmap(2) implementation understands
> implications of MAP_SYNC flag and that's all that's needed to set
> .mmap_supported_flags.

Good point.

Also, that check will need to be updated when the pmem-virtio patchset goes
in.

> > Signed-off-by: Adam Borowski <kilobyte@angband.pl>
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > ---
> >  fs/btrfs/file.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 9d5a3c99a6b9..362a9cf9dcb2 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/btrfs.h>
> >  #include <linux/uio.h>
> >  #include <linux/iversion.h>
> > +#include <linux/mman.h>
> >  #include "ctree.h"
> >  #include "disk-io.h"
> >  #include "transaction.h"
> > @@ -3319,6 +3320,9 @@ const struct file_operations btrfs_file_operations = {
> >  	.splice_read	= generic_file_splice_read,
> >  	.write_iter	= btrfs_file_write_iter,
> >  	.mmap		= btrfs_file_mmap,
> > +#ifdef CONFIG_FS_DAX
> > +	.mmap_supported_flags = MAP_SYNC,
> > +#endif
> >  	.open		= btrfs_file_open,
> >  	.release	= btrfs_release_file,
> >  	.fsync		= btrfs_sync_file,
> > -- 
> > 2.16.4
> > 
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
> 

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