On Tue, Aug 15, 2017 at 5:27 AM, Jan Kara <jack@xxxxxxx> wrote: > On Mon 14-08-17 23:12:16, Dan Williams wrote: >> The mmap syscall suffers from the ABI anti-pattern of not validating >> unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT need a >> mechanism to define new behavior that is known to fail on older kernels >> without the feature. Use the fact that specifying MAP_SHARED and >> MAP_PRIVATE at the same time is invalid as a cute hack to allow a new >> set of validated flags to be introduced. >> >> This also introduces the ->fmmap() file operation that is ->mmap() plus >> flags. Each ->fmmap() implementation must fail requests when a locally >> unsupported flag is specified. > ... >> diff --git a/include/linux/fs.h b/include/linux/fs.h >> index 1104e5df39ef..bbe755d0caee 100644 >> --- a/include/linux/fs.h >> +++ b/include/linux/fs.h >> @@ -1674,6 +1674,7 @@ struct file_operations { >> long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); >> long (*compat_ioctl) (struct file *, unsigned int, unsigned long); >> int (*mmap) (struct file *, struct vm_area_struct *); >> + int (*fmmap) (struct file *, struct vm_area_struct *, unsigned long); >> int (*open) (struct inode *, struct file *); >> int (*flush) (struct file *, fl_owner_t id); >> int (*release) (struct inode *, struct file *); >> @@ -1748,6 +1749,12 @@ static inline int call_mmap(struct file *file, struct vm_area_struct *vma) >> return file->f_op->mmap(file, vma); >> } >> >> +static inline int call_fmmap(struct file *file, struct vm_area_struct *vma, >> + unsigned long flags) >> +{ >> + return file->f_op->fmmap(file, vma, flags); >> +} >> + > > Hum, I dislike a new file op for this when the only problem with ->mmap is > that it misses 'flags' argument. I understand there are lots of ->mmap > implementations out there and modifying prototype of them all is painful > but is it so bad? Coccinelle patch for this should be rather easy... So it wasn't all that easy, and Linus declined to take it. I think we should add a new ->mmap_validate() file operation and save the tree-wide cleanup until later. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>