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From: Jia He <justin.he@arm.com>
To: Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Jonathan Corbet <corbet@lwn.net>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Eric Biggers <ebiggers@google.com>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	Matthew Wilcox <willy@infradead.org>, Jia He <justin.he@arm.com>
Subject: [PATCH RFCv4 2/4] lib/vsprintf.c: make '%pD' print full path for file
Date: Tue, 15 Jun 2021 23:49:50 +0800	[thread overview]
Message-ID: <20210615154952.2744-3-justin.he@arm.com> (raw)
In-Reply-To: <20210615154952.2744-1-justin.he@arm.com>

Previously, the specifier '%pD' is for printing dentry name of struct
file. It may not be perfect (by default it only prints one component.)

As suggested by Linus at [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 full path of that file.

Precision is never going to be used with %p (or any of its kernel
extensions) if -Wformat is turned on.
.

[1] https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@mail.gmail.com/

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jia He <justin.he@arm.com>
---
 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/dcache.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 */
+	if (buf >= end)
+		return buf + reserved_size;
+
+	/*
+	 * case 2: small scratch space for long d_path name. The space
+	 * [buf,end] has been filled with truncated string. Hence use the
+	 * full dpath_len for further string widening.
+	 */
+	if (prepend_len < 0)
+		return widen_string(buf + dpath_len, dpath_len, end, spec);
+
+	/* case3: space is big enough */
+	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


  parent reply	other threads:[~2021-06-15 15:51 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 15:49 [PATCH RFCv4 0/4] make '%pD' print full path for file Jia He
2021-06-15 15:49 ` [PATCH RFCv4 1/4] fs: introduce helper d_path_unsafe() Jia He
2021-06-15 20:40   ` Andy Shevchenko
2021-06-16  0:54     ` Justin He
2021-06-15 15:49 ` Jia He [this message]
2021-06-15 20:44   ` [PATCH RFCv4 2/4] lib/vsprintf.c: make '%pD' print full path for file Andy Shevchenko
2021-06-17 14:09   ` Petr Mladek
2021-06-22  2:20     ` Justin He
2021-06-15 15:49 ` [PATCH RFCv4 3/4] lib/test_printf.c: split write-beyond-buffer check in two Jia He
2021-06-17 14:17   ` Petr Mladek
2021-06-15 15:49 ` [PATCH RFCv4 4/4] lib/test_printf.c: add test cases for '%pD' Jia He
2021-06-15 20:47   ` Andy Shevchenko
2021-06-17 14:52     ` Petr Mladek
2021-06-22  2:21       ` Justin He
2021-06-15 20:42 ` [PATCH RFCv4 0/4] make '%pD' print full path for file Andy Shevchenko
2021-06-16  5:09 ` Christoph Hellwig
2021-06-16  5:16   ` Justin He

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