Previously, the specifier '%pD' was for printing dentry name of struct
file. It may not be perfect since by default it only prints one component.
As suggested by Linus [1]:
A dentry has a parent, but at the same time, a dentry really does
inherently have "one name" (and given just the dentry pointers, you
can't show mount-related parenthood, so in many ways the "show just
one name" makes sense for "%pd" in ways it doesn't necessarily for
"%pD"). But while a dentry arguably has that "one primary component",
a _file_ is certainly not exclusively about that last component.
Hence change the behavior of '%pD' to print the full path of that file.
It is worthy of noting that %pD uses the entire given buffer as a scratch
space. It might write something behind the trailing '\0' but never write
beyond the scratch space.
Precision specifier is never going to be used with %p (or any of its
kernel extensions) if -Wformat is turned on.
Link: https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@mail.gmail.com/ [1]
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Jia He <[email protected]>
---
Documentation/core-api/printk-formats.rst | 7 ++--
lib/vsprintf.c | 40 ++++++++++++++++++++---
2 files changed, 41 insertions(+), 6 deletions(-)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index d941717a191b..15d6f1057b66 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -418,12 +418,15 @@ 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. %pD uses the entire given buffer as a scratch space. It might
+write something behind the trailing '\0' but never write beyond the
+scratch space.
Passed by reference.
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 26c83943748a..e65799292745 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -26,6 +26,7 @@
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
+#include <linux/dcache.h>
#include <linux/kernel.h>
#include <linux/kallsyms.h>
#include <linux/math64.h>
@@ -947,13 +948,44 @@ 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)
{
+ int prepend_len, widen_len, dpath_len;
+ const struct path *path;
+ char *p;
+
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;
+
+ widen_len = max_t(int, dpath_len, spec.field_width);
+
+ /* Case 1: Already started past the buffer. Just forward @buf. */
+ if (buf >= end)
+ return buf + widen_len;
+
+ /*
+ * Case 2: The entire remaining space of the buffer filled by
+ * the truncated path. Still need to get moved right when
+ * the field width is greater than the full path length.
+ */
+ if (prepend_len < 0)
+ return widen_string(buf + dpath_len, dpath_len, end, spec);
+
+ /*
+ * Case 3: The full path is printed at the end of the buffer.
+ * Print it at the right location in the same buffer.
+ */
+ return string_nocheck(buf, end, p, spec);
}
#ifdef CONFIG_BLOCK
static noinline_for_stack
@@ -2341,7 +2373,7 @@ 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 the full path name of a struct file
* - 'g' For block_device name (gendisk + partition number)
* - 't[RT][dt][r][s]' For time and date as represented by:
* R struct rtc_time
@@ -2440,7 +2472,7 @@ 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
On Thu 2021-07-15 09:14:05, Jia He wrote:
> Previously, the specifier '%pD' was for printing dentry name of struct
> file. It may not be perfect since by default it only prints one component.
>
> As suggested by Linus [1]:
> A dentry has a parent, but at the same time, a dentry really does
> inherently have "one name" (and given just the dentry pointers, you
> can't show mount-related parenthood, so in many ways the "show just
> one name" makes sense for "%pd" in ways it doesn't necessarily for
> "%pD"). But while a dentry arguably has that "one primary component",
> a _file_ is certainly not exclusively about that last component.
>
> Hence change the behavior of '%pD' to print the full path of that file.
> It is worthy of noting that %pD uses the entire given buffer as a scratch
> space. It might write something behind the trailing '\0' but never write
> beyond the scratch space.
>
> Precision specifier is never going to be used with %p (or any of its
> kernel extensions) if -Wformat is turned on.
>
> Link: https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@mail.gmail.com/ [1]
> Suggested-by: Linus Torvalds <[email protected]>
> Signed-off-by: Jia He <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Best Regards,
Petr