[PATCH] um: Use swap() instead of open coding it

[kernel test robot]

Hi Jiapeng,

kernel test robot noticed the following build errors:

[auto build test ERROR on wireless-next/main]
[also build test ERROR on linus/master v6.7-rc2 next-20231122]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Jiapeng-Chong/um-Use-swap-instead-of-open-coding-it/20231122-113031
base:   https://git.kernel.org/pub/scm/linux/kernel/git/wireless/wireless-next.git main
patch link:    https://lore.kernel.org/r/20231122032518.53305-1-jiapeng.chong%40linux.alibaba.com
patch subject: [PATCH] um: Use swap() instead of open coding it
config: um-randconfig-001-20231122 (https://download.01.org/0day-ci/archive/20231123/202311230538.6Fd2FqkL-lkp@intel.com/config)
compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231123/202311230538.6Fd2FqkL-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp at intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202311230538.6Fd2FqkL-lkp@intel.com/

All errors (new ones prefixed by >>):

>> arch/um/os-Linux/sigio.c:80:5: error: call to undeclared function 'swap'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
                                   swap(current_poll, next_poll);
                                   ^
   arch/um/os-Linux/sigio.c:80:5: note: did you mean 'swab'?
   /usr/include/unistd.h:1168:13: note: 'swab' declared here
   extern void swab (const void *__restrict __from, void *__restrict __to,
               ^
   1 error generated.


vim +/swap +80 arch/um/os-Linux/sigio.c

    50	
    51	static int write_sigio_thread(void *unused)
    52	{
    53		struct pollfds *fds;
    54		struct pollfd *p;
    55		int i, n, respond_fd;
    56		char c;
    57	
    58		os_fix_helper_signals();
    59		fds = &current_poll;
    60		while (1) {
    61			n = poll(fds->poll, fds->used, -1);
    62			if (n < 0) {
    63				if (errno == EINTR)
    64					continue;
    65				printk(UM_KERN_ERR "write_sigio_thread : poll returned "
    66				       "%d, errno = %d\n", n, errno);
    67			}
    68			for (i = 0; i < fds->used; i++) {
    69				p = &fds->poll[i];
    70				if (p->revents == 0)
    71					continue;
    72				if (p->fd == sigio_private[1]) {
    73					CATCH_EINTR(n = read(sigio_private[1], &c,
    74							     sizeof(c)));
    75					if (n != sizeof(c))
    76						printk(UM_KERN_ERR
    77						       "write_sigio_thread : "
    78						       "read on socket failed, "
    79						       "err = %d\n", errno);
  > 80					swap(current_poll, next_poll);
    81					respond_fd = sigio_private[1];
    82				}
    83				else {
    84					respond_fd = write_sigio_fds[1];
    85					fds->used--;
    86					memmove(&fds->poll[i], &fds->poll[i + 1],
    87						(fds->used - i) * sizeof(*fds->poll));
    88				}
    89	
    90				CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
    91				if (n != sizeof(c))
    92					printk(UM_KERN_ERR "write_sigio_thread : "
    93					       "write on socket failed, err = %d\n",
    94					       errno);
    95			}
    96		}
    97	
    98		return 0;
    99	}
   100	

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