> if (file) {
> struct inode *inode = file_inode(file);
> + unsigned long flags_mask = file->f_op->mmap_supported_flags;
> +
> + if (!flags_mask)
> + flags_mask = LEGACY_MAP_MASK;
>
> switch (flags & MAP_TYPE) {
> case MAP_SHARED:
> + /*
> + * Silently ignore unsupported flags - MAP_SHARED has
> + * traditionally behaved like that and we don't want
> + * to break compatibility.
> + */
> + flags &= flags_mask;
> + /*
> + * Force use of MAP_SHARED_VALIDATE with non-legacy
> + * flags. E.g. MAP_SYNC is dangerous to use with
> + * MAP_SHARED as you don't know which consistency model
> + * you will get.
> + */
> + flags &= LEGACY_MAP_MASK;
> + /* fall through */
> + case MAP_SHARED_VALIDATE:
> + if (flags & ~flags_mask)
> + return -EOPNOTSUPP;
Hmmm. I'd expect this to worth more like:
case MAP_SHARED:
/* Ignore all new flags that need validation: */
flags &= LEGACY_MAP_MASK;
/*FALLTHROUGH*/
case MAP_SHARED_VALIDATE:
if (flags & ~file->f_op->mmap_supported_flags)
return -EOPNOTSUPP;
with the legacy mask always implicitly support as indicated in my
comment to the XFS patch.
Although even the ignoring in MAP_SHARED seems dangerous, but I guess
we need that to keep strict backwards compatibility. In world I'd
rather do
case MAP_SHARED:
if (flags & ~LEGACY_MAP_MASK)
return -EINVAL;
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