On Thu, Oct 12, 2017 at 6:42 AM, Jan Kara <jack@xxxxxxx> wrote:
> On Wed 11-10-17 15:11:21, Dan Williams wrote:
>> On Wed, Oct 11, 2017 at 1:06 PM, Jan Kara <jack@xxxxxxx> wrote:
>> > Now when everything is prepared, add support in ext4 to accept MAP_SYNC
>> > as an mmap(2) flag.
>> >
>> > Signed-off-by: Jan Kara <jack@xxxxxxx>
>> > ---
>> > fs/ext4/file.c | 20 ++++++++++++++++++++
>> > 1 file changed, 20 insertions(+)
>> >
>> > diff --git a/fs/ext4/file.c b/fs/ext4/file.c
>> > index 61a8788168f3..f013cda84b3d 100644
>> > --- a/fs/ext4/file.c
>> > +++ b/fs/ext4/file.c
>> > @@ -364,6 +364,25 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
>> > return 0;
>> > }
>> >
>> > +#define EXT4_SUPPORTED_MAP_FLAGS (LEGACY_MAP_MASK | MAP_SYNC)
>> > +
>> > +static int ext4_file_mmap_validate(struct file *file,
>> > + struct vm_area_struct *vma,
>> > + unsigned long map_flags)
>> > +{
>> > + if (map_flags & ~EXT4_SUPPORTED_MAP_FLAGS)
>> > + return -EOPNOTSUPP;
>> > +
>> > + /*
>> > + * 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(file)) && (map_flags & MAP_SYNC))
>> > + return -EOPNOTSUPP;
>>
>> Perhaps EPERM instead to differentiate the unsupported flags case?
>> There's precedent for mmap returning EPERM for reasons other than
>> incompatible PROT flags.
>
> Hum, I could make it EINVAL. EPERM looks just too bogus to me.
EINVAL is indistinguishable from a kernel that does not support
MAP_SHARED_VALIDATE...
