On Fri, Sep 26, 2025 at 4:37 PM Michael S. Tsirkin <[email protected]> wrote: > > On Fri, Sep 26, 2025 at 12:14:26PM +0200, Eugenio Pérez wrote: > > PATCH v5: > > * Properly return errno if copy_to_user returns >0 in VDUSE_IOTLB_GET_FD > > ioctl (Jason). > > ??? > > I think copy_to_user returns an unsigned value: the number of bytes copied. > > > static __always_inline unsigned long __must_check > copy_from_user(void *to, const void __user *from, unsigned long n) > { > if (!check_copy_size(to, n, false)) > return n; > #ifdef INLINE_COPY_FROM_USER > return _inline_copy_from_user(to, from, n); > #else > return _copy_from_user(to, from, n); > #endif > } > > > so, how does the patch work then? >
copy_from_user returns the number of bytes that could not be copied. For example when the object size in the kernel is less than n bytes long, check_copy_size returns false and copy_from_user returns n, the amount of size requested to copy.
