Documentation/vm/page-types.c: auto debugfs mount for hwpoison operation

page-types.c doesn't supply a way to specify the debugfs path and the
original debugfs path is not usual on most machines.  This patch supplies
a way to auto mount debugfs if needed.

This patch is heavily inspired by tools/perf/utils/debugfs.c

[akpm@linux-foundation.org: make functions static]
[akpm@linux-foundation.org: fix debugfs_mount() signature]
Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 101 insertions, 4 deletions

diff --git a/Documentation/vm/page-types.c b/Documentation/vm/page-types.c
index cc96ee2666f2..7445caa26d05 100644
--- a/Documentation/vm/page-types.c
+++ b/Documentation/vm/page-types.c
@@ -32,8 +32,20 @@
 #include <sys/types.h>
 #include <sys/errno.h>
 #include <sys/fcntl.h>
+#include <sys/mount.h>
+#include <sys/statfs.h>
+#include "../../include/linux/magic.h"
 
 
+#ifndef MAX_PATH
+# define MAX_PATH 256
+#endif
+
+#ifndef STR
+# define _STR(x) #x
+# define STR(x) _STR(x)
+#endif
+
 /*
  * pagemap kernel ABI bits
  */
@@ -152,6 +164,12 @@ static const char *page_flag_names[] = {
 };
 
 
+static const char *debugfs_known_mountpoints[] = {
+        "/sys/kernel/debug",
+        "/debug",
+        0,
+};
+
 /*
  * data structures
  */
@@ -184,7 +202,7 @@ static int		kpageflags_fd;
 static int              opt_hwpoison;
 static int              opt_unpoison;
 
-static const char       hwpoison_debug_fs[] = "/debug/hwpoison";
+static char             hwpoison_debug_fs[MAX_PATH+1];
 static int              hwpoison_inject_fd;
 static int              hwpoison_forget_fd;
 
@@ -464,21 +482,100 @@ static uint64_t kpageflags_flags(uint64_t flags)
         return flags;
 }
 
+/* verify that a mountpoint is actually a debugfs instance */
+static int debugfs_valid_mountpoint(const char *debugfs)
+{
+        struct statfs st_fs;
+
+        if (statfs(debugfs, &st_fs) < 0)
+                return -ENOENT;
+        else if (st_fs.f_type != (long) DEBUGFS_MAGIC)
+                return -ENOENT;
+
+        return 0;
+}
+
+/* find the path to the mounted debugfs */
+static const char *debugfs_find_mountpoint(void)
+{
+        const char **ptr;
+        char type[100];
+        FILE *fp;
+
+        ptr = debugfs_known_mountpoints;
+        while (*ptr) {
+                if (debugfs_valid_mountpoint(*ptr) == 0) {
+                        strcpy(hwpoison_debug_fs, *ptr);
+                        return hwpoison_debug_fs;
+                }
+                ptr++;
+        }
+
+        /* give up and parse /proc/mounts */
+        fp = fopen("/proc/mounts", "r");
+        if (fp == NULL)
+                perror("Can't open /proc/mounts for read");
+
+        while (fscanf(fp, "%*s %"
+                      STR(MAX_PATH)
+                      "s %99s %*s %*d %*d\n",
+                      hwpoison_debug_fs, type) == 2) {
+                if (strcmp(type, "debugfs") == 0)
+                        break;
+        }
+        fclose(fp);
+
+        if (strcmp(type, "debugfs") != 0)
+                return NULL;
+
+        return hwpoison_debug_fs;
+}
+
+/* mount the debugfs somewhere if it's not mounted */
+
+static void debugfs_mount(void)
+{
+        const char **ptr;
+
+        /* see if it's already mounted */
+        if (debugfs_find_mountpoint())
+                return;
+
+        ptr = debugfs_known_mountpoints;
+        while (*ptr) {
+                if (mount(NULL, *ptr, "debugfs", 0, NULL) == 0) {
+                        /* save the mountpoint */
+                        strcpy(hwpoison_debug_fs, *ptr);
+                        break;
+                }
+                ptr++;
+        }
+
+        if (*ptr == NULL) {
+                perror("mount debugfs");
+                exit(EXIT_FAILURE);
+        }
+}
+
 /*
  * page actions
  */
 
 static void prepare_hwpoison_fd(void)
 {
-        char buf[100];
+        char buf[MAX_PATH + 1];
+
+        debugfs_mount();
 
         if (opt_hwpoison && !hwpoison_inject_fd) {
-                sprintf(buf, "%s/corrupt-pfn", hwpoison_debug_fs);
+                snprintf(buf, MAX_PATH, "%s/hwpoison/corrupt-pfn",
+                        hwpoison_debug_fs);
                 hwpoison_inject_fd = checked_open(buf, O_WRONLY);
         }
 
         if (opt_unpoison && !hwpoison_forget_fd) {
-                sprintf(buf, "%s/unpoison-pfn", hwpoison_debug_fs);
+                snprintf(buf, MAX_PATH, "%s/hwpoison/unpoison-pfn",
+                        hwpoison_debug_fs);
                 hwpoison_forget_fd = checked_open(buf, O_WRONLY);
         }
 }