Diego Nieto Cid, le mar. 31 déc. 2024 20:48:08 +0000, a ecrit:
> On Tue, Dec 31, 2024 at 08:32:47PM +0000, Diego Nieto Cid wrote:
> >
> > Adding the following line to the program:
> >
> > printf("cmsghdr: %lu\n", sizeof (struct cmsghdr));
> >
> > shows 12 on Hurd and 16 on Linux. I think I'm closer :)
>
> The only difference in the structure definition is the cmsg_len field type
> which happens to be the 4 missing bytes.
>
> --- >8 --- >8 ---
> Linux
> =====
>
> /* Structure used for storage of ancillary data object information. */
> struct cmsghdr
> {
> size_t cmsg_len; /* Length of data in cmsg_data plus length
> of cmsghdr structure.
> !! The type should be socklen_t but the
> definition of the kernel is
> incompatible
> with this. */
> int cmsg_level; /* Originating protocol. */
> int cmsg_type; /* Protocol specific type. */
> #if __glibc_c99_flexarr_available
> __extension__ unsigned char __cmsg_data __flexarr; /* Ancillary data.
> */
> #endif
> };
>
> Hurd
> ====
>
> /* Structure used for storage of ancillary data object information. */
> struct cmsghdr
> {
> socklen_t cmsg_len; /* Length of data in cmsg_data plus length
> of cmsghdr structure. */
That's the correct type according to posix:
./basedefs/sys_socket.h.html:<tt>socklen_t cmsg_len </tt> Data byte count,
including the <b>cmsghdr</b>. <tt>
> int cmsg_level; /* Originating protocol. */
> int cmsg_type; /* Protocol specific type. */
> #if __glibc_c99_flexarr_available
> __extension__ unsigned char __cmsg_data __flexarr; /* Ancillary data.
> */
> #endif
> };
> --- >8 --- >8 ---
