add formats for dentry/file pathnames

New formats: %p[dD][234]?.  The next pointer is interpreted as struct dentry *
or struct file * resp. ('d' => dentry, 'D' => file) and the last component(s)
of pathname are printed (%pd => just the last one, %pd2 => the last two, etc.)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 91 insertions, 0 deletions

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 3e8cb73ac43c..9552a3299ec9 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -168,6 +168,15 @@ UUID/GUID addresses:
         Where no additional specifiers are used the default little endian
         order with lower case hex characters will be printed.
 
+dentry names:
+        %pd{,2,3,4}
+        %pD{,2,3,4}
+
+        For printing dentry name; if we race with d_move(), the name might be
+        a mix of old and new ones, but it won't oops.  %pd dentry is a safer
+        equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
+        n last components.  %pD does the same thing for struct file.
+
 struct va_format:
 
         %pV
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 739a36366b79..26559bdb4c49 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -26,6 +26,7 @@
 #include <linux/math64.h>
 #include <linux/uaccess.h>
 #include <linux/ioport.h>
+#include <linux/dcache.h>
 #include <net/addrconf.h>
 
 #include <asm/page.h>           /* for PAGE_SIZE */
@@ -532,6 +533,81 @@ char *string(char *buf, char *end, const char *s, struct printf_spec spec)
         return buf;
 }
 
+static void widen(char *buf, char *end, unsigned len, unsigned spaces)
+{
+        size_t size;
+        if (buf >= end) /* nowhere to put anything */
+                return;
+        size = end - buf;
+        if (size <= spaces) {
+                memset(buf, ' ', size);
+                return;
+        }
+        if (len) {
+                if (len > size - spaces)
+                        len = size - spaces;
+                memmove(buf + spaces, buf, len);
+        }
+        memset(buf, ' ', spaces);
+}
+
+static noinline_for_stack
+char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_spec spec,
+                  const char *fmt)
+{
+        const char *array[4], *s;
+        const struct dentry *p;
+        int depth;
+        int i, n;
+
+        switch (fmt[1]) {
+                case '2': case '3': case '4':
+                        depth = fmt[1] - '0';
+                        break;
+                default:
+                        depth = 1;
+        }
+
+        rcu_read_lock();
+        for (i = 0; i < depth; i++, d = p) {
+                p = ACCESS_ONCE(d->d_parent);
+                array[i] = ACCESS_ONCE(d->d_name.name);
+                if (p == d) {
+                        if (i)
+                                array[i] = "";
+                        i++;
+                        break;
+                }
+        }
+        s = array[--i];
+        for (n = 0; n != spec.precision; n++, buf++) {
+                char c = *s++;
+                if (!c) {
+                        if (!i)
+                                break;
+                        c = '/';
+                        s = array[--i];
+                }
+                if (buf < end)
+                        *buf = c;
+        }
+        rcu_read_unlock();
+        if (n < spec.field_width) {
+                /* we want to pad the sucker */
+                unsigned spaces = spec.field_width - n;
+                if (!(spec.flags & LEFT)) {
+                        widen(buf - n, end, n, spaces);
+                        return buf + spaces;
+                }
+                while (spaces--) {
+                        if (buf < end)
+                                *buf = ' ';
+                        ++buf;
+                }
+        }
+        return buf;
+}
+
 static noinline_for_stack
 char *symbol_string(char *buf, char *end, void *ptr,
                     struct printf_spec spec, const char *fmt)
@@ -1253,6 +1329,12 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
                 spec.base = 16;
                 return number(buf, end,
                               (unsigned long long) *((phys_addr_t *)ptr), spec);
+        case 'd':
+                return dentry_name(buf, end, ptr, spec, fmt);
+        case 'D':
+                return dentry_name(buf, end,
+                                   ((const struct file *)ptr)->f_path.dentry,
+                                   spec, fmt);
         }
         spec.flags |= SMALL;
         if (spec.field_width == -1) {