Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jia He <redacted>
---
 Documentation/core-api/printk-formats.rst |  5 +--
 lib/vsprintf.c                            | 37 ++++++++++++++++++++---
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index f063a384c7c8..95ba14dc529b 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst

@@ -408,12 +408,13 @@ dentry names
 ::

        %pd{,2,3,4}
-       %pD{,2,3,4}
+       %pD

 For printing dentry name; if we race with :c:func:`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.
+last components.  %pD prints full file path together with mount-related
+parenthood.

 Passed by reference.

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index f0c35d9b65bf..9d3166332726 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c

@@ -27,6 +27,7 @@
 #include <linux/string.h>
 #include <linux/ctype.h>
 #include <linux/kernel.h>

 #include <linux/kallsyms.h>
 #include <linux/math64.h>
 #include <linux/uaccess.h>

@@ -920,13 +921,41 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp
 }

 static noinline_for_stack
-char *file_dentry_name(char *buf, char *end, const struct file *f,
+char *file_d_path_name(char *buf, char *end, const struct file *f,
                        struct printf_spec spec, const char *fmt)
 {
+       const struct path *path;
+       char *p;
+       int prepend_len, reserved_size, dpath_len;
+
        if (check_pointer(&buf, end, f, spec))
                return buf;

-       return dentry_name(buf, end, f->f_path.dentry, spec, fmt);
+       path = &f->f_path;
+       if (check_pointer(&buf, end, path, spec))
+               return buf;
+
+       p = d_path_unsafe(path, buf, end - buf, &prepend_len);
+
+       /* Calculate the full d_path length, ignoring the tail '\0' */
+       dpath_len = end - buf - prepend_len - 1;
+
+       reserved_size = max_t(int, dpath_len, spec.field_width);
+
+       /* case 1: no space at all, forward the buf with reserved size */

+       return string_nocheck(buf, end, p, spec);
 }
 #ifdef CONFIG_BLOCK
 static noinline_for_stack

@@ -2296,7 +2325,7 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
  * - 'a[pd]' For address types [p] phys_addr_t, [d] dma_addr_t and derivatives
  *           (default assumed to be phys_addr_t, passed by reference)
  * - 'd[234]' For a dentry name (optionally 2-4 last components)
- * - 'D[234]' Same as 'd' but for a struct file
+ * - 'D' For full path name of a struct file
  * - 'g' For block_device name (gendisk + partition number)
  * - 't[RT][dt][r]' For time and date as represented by:
  *      R    struct rtc_time

@@ -2395,7 +2424,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
        case 'C':
                return clock(buf, end, ptr, spec, fmt);
        case 'D':
-               return file_dentry_name(buf, end, ptr, spec, fmt);
+               return file_d_path_name(buf, end, ptr, spec, fmt);
 #ifdef CONFIG_BLOCK
        case 'g':
                return bdev_name(buf, end, ptr, spec, fmt);
--

2.17.1