Increase FD_SETSIZE to 256

[Chris Johns]

The default for FD_SETSIZE in newlib is 64. This is proving to be too small for EPICS applications. EPICS limits the number of descriptors ​here for RTEMS 6 builds. The comment in EPICS base is:

/* Note: The select() system call can only be used with the first FD_SETSIZE
 *       File Descriptors (newlib default is 64).  Beginning RTEMS 5.1, FDs are
 *       allocated sequentially.  So changing this CONFIGURE parameter such
 *       that CONFIGURE_MAXIMUM_FILE_DESCRIPTORS >= FD_SETSIZE will likely
 *       cause applications making select() calls to fault at some point.
 *
 *       IOC core components (libca and RSRV) do not make select() calls.
 *
 *       Applications and driver code using poll() or other socket
 *       multiplexers do not share this limitation.
 *
 *       cf. https://github.com/epics-base/epics-base/issues/300
 */

Increasing FD_SETSIZE to 256 will increase the set but 64 is too small for RTEMS and we do not need 1024 that systems like FreeBSD have.

[Chris Johns]

Newlib patch to increase the FD_SETSIZE from 64 to 256 bits per set

[Chris Johns]

RSB patch to apply the newlib patch. Please use for testing.

[Chris Johns]

LibBSD select() call is ​https://git.rtems.org/rtems-libbsd/tree/freebsd/sys/kern/sys_generic.c?h=6-freebsd-12#n998 and it says:

/*
 * The magic 2048 here is chosen to be just enough for FD_SETSIZE
 * infds with the new FD_SETSIZE of 1024, and more than enough for
 * FD_SETSIZE infds, outfds and exceptfds with the old FD_SETSIZE
 * of 256.
 */

[Joel Sherrill]

Patch submitted to newlib. When I get acked to push it, I will let you know so you can bump the newlib hash to pick the change to 256 up.