Re: [PATCH 01/17] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags

> 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;