Hi Vlastimil,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kees/for-next/pstore]
[also build test WARNING on linus/master linux/master v5.6 next-20200330]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Vlastimil-Babka/support-setting-sysctl-parameters-from-kernel-command-line/20200331-023453
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/pstore
config: um-i386_defconfig (attached as .config)
compiler: gcc-7 (Debian 7.4.0-6) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=um SUBARCH=i386

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/printk.h:7:0,
                    from include/linux/kernel.h:15,
                    from include/linux/list.h:9,
                    from include/linux/sysctl.h:25,
                    from fs/proc/proc_sysctl.c:6:
   fs/proc/proc_sysctl.c: In function 'process_sysctl_arg':
   include/linux/kern_levels.h:5:18: warning: format '%ld' expects argument of type 'long int', but argument 2 has type 'ssize_t {aka int}' [-Wformat=]
    #define KERN_SOH "\001"  /* ASCII Start Of Header */
                     ^
   include/linux/kern_levels.h:11:18: note: in expansion of macro 'KERN_SOH'
    #define KERN_ERR KERN_SOH "3" /* error conditions */
                     ^~~~~~~~
   include/linux/printk.h:304:9: note: in expansion of macro 'KERN_ERR'
     printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__)
            ^~~~~~~~
>> fs/proc/proc_sysctl.c:1798:3: note: in expansion of macro 'pr_err'
      pr_err("Wrote only %ld bytes of %d writing to proc file %s to set sysctl parameter '%s=%s'",
      ^~~~~~
   fs/proc/proc_sysctl.c:1798:24: note: format string is defined here
      pr_err("Wrote only %ld bytes of %d writing to proc file %s to set sysctl parameter '%s=%s'",
                         ~~^
                         %d

vim +/pr_err +1798 fs/proc/proc_sysctl.c

  1729	
  1730	/* Set sysctl value passed on kernel command line. */
  1731	static int process_sysctl_arg(char *param, char *val,
  1732				       const char *unused, void *arg)
  1733	{
  1734		char *path;
  1735		struct vfsmount *proc_mnt = *((struct vfsmount **)arg);
  1736		struct file_system_type *proc_fs_type;
  1737		struct file *file;
  1738		int len;
  1739		int err;
  1740		loff_t pos = 0;
  1741		ssize_t wret;
  1742	
  1743		if (strncmp(param, "sysctl", sizeof("sysctl") - 1))
  1744			return 0;
  1745	
  1746		param += sizeof("sysctl") - 1;
  1747	
  1748		if (param[0] != '/' && param[0] != '.')
  1749			return 0;
  1750	
  1751		param++;
  1752	
  1753		if (!proc_mnt) {
  1754			proc_fs_type = get_fs_type("proc");
  1755			if (!proc_fs_type) {
  1756				pr_err("Failed to find procfs to set sysctl from command line");
  1757				return 0;
  1758			}
  1759			proc_mnt = kern_mount(proc_fs_type);
  1760			put_filesystem(proc_fs_type);
  1761			if (IS_ERR(proc_mnt)) {
  1762				pr_err("Failed to mount procfs to set sysctl from command line");
  1763				return 0;
  1764			}
  1765			*((struct vfsmount **)arg) = proc_mnt;
  1766		}
  1767	
  1768		path = kasprintf(GFP_KERNEL, "sys/%s", param);
  1769		if (!path)
  1770			panic("%s: Failed to allocate path for %s\n", __func__, param);
  1771		strreplace(path, '.', '/');
  1772	
  1773		file = file_open_root(proc_mnt->mnt_root, proc_mnt, path, O_WRONLY, 0);
  1774		if (IS_ERR(file)) {
  1775			err = PTR_ERR(file);
  1776			if (err == -ENOENT)
  1777				pr_err("Failed to set sysctl parameter '%s=%s': parameter not found",
  1778					param, val);
  1779			else if (err == -EACCES)
  1780				pr_err("Failed to set sysctl parameter '%s=%s': permission denied (read-only?)",
  1781					param, val);
  1782			else
  1783				pr_err("Error %pe opening proc file to set sysctl parameter '%s=%s'",
  1784					file, param, val);
  1785			goto out;
  1786		}
  1787		len = strlen(val);
  1788		wret = kernel_write(file, val, len, &pos);
  1789		if (wret < 0) {
  1790			err = wret;
  1791			if (err == -EINVAL)
  1792				pr_err("Failed to set sysctl parameter '%s=%s': invalid value",
  1793					param, val);
  1794			else
  1795				pr_err("Error %pe writing to proc file to set sysctl parameter '%s=%s'",
  1796					ERR_PTR(err), param, val);
  1797		} else if (wret != len) {
> 1798			pr_err("Wrote only %ld bytes of %d writing to proc file %s to set sysctl parameter '%s=%s'",
  1799				wret, len, path, param, val);
  1800		}
  1801	
  1802		err = filp_close(file, NULL);
  1803		if (err)
  1804			pr_err("Error %pe closing proc file to set sysctl parameter '%s=%s'",
  1805				ERR_PTR(err), param, val);
  1806	out:
  1807		kfree(path);
  1808		return 0;
  1809	}
  1810	

---
0-DAY CI Kernel Test Service, Intel Corporation
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