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From: Dmitry Monakhov <dmonakhov@openvz.org>
To: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, axboe@kernel.dk, viro@zeniv.linux.org.uk,
        dm-devel@redhat.com, Dmitry Monakhov <dmonakhov@openvz.org>
Subject: [PATCH 2/7] lib/vsprintf: add %*pg format specifier
Date: Fri, 17 Apr 2015 12:29:14 +0400
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This allow to directly print block_device name.
Currently one should use bdevname() with temporal char buffer.
This is very ineffective because bloat stack usage for deep IO call-traces

Example:
	%pg  ->    sda, sda1 or loop0p1

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 Documentation/printk-formats.txt |    6 ++++++
 lib/vsprintf.c                   |   28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 5a615c1..de2f18f 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -216,6 +216,12 @@ dentry names:
 	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.
 
+block_device names:
+
+	%pg	sda, sda1 or loop0p1
+
+	For printing name of block_device pointers.
+
 struct va_format:
 
 	%pV
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b235c96..57f6fa9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -29,6 +29,9 @@
 #include <linux/dcache.h>
 #include <linux/cred.h>
 #include <net/addrconf.h>
+#ifdef CONFIG_BLOCK
+#include <linux/blkdev.h>
+#endif
 
 #include <asm/page.h>		/* for PAGE_SIZE */
 #include <asm/sections.h>	/* for dereference_function_descriptor() */
@@ -610,6 +613,23 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp
 	return buf;
 }
 
+#ifdef CONFIG_BLOCK
+static noinline_for_stack
+char *bdev_name(char *buf, char *end, struct block_device *bdev,
+		struct printf_spec spec, const char *fmt)
+{
+	struct gendisk *hd = bdev->bd_disk;
+	
+	buf = string(buf, end, hd->disk_name, spec);
+	if (bdev->bd_part->partno) {
+		if (isdigit(hd->disk_name[strlen(hd->disk_name)-1]) && buf < end)
+			*buf++ = 'p';
+		buf = number(buf, end, bdev->bd_part->partno, spec);
+	}
+	return buf;
+}
+#endif
+
 static noinline_for_stack
 char *symbol_string(char *buf, char *end, void *ptr,
 		    struct printf_spec spec, const char *fmt)
@@ -1404,6 +1424,8 @@ int kptr_restrict __read_mostly;
  *           (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
+ * - 'g' For block_device name (gendisk + partition number)
+
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
@@ -1552,6 +1574,11 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		return dentry_name(buf, end,
 				   ((const struct file *)ptr)->f_path.dentry,
 				   spec, fmt);
+#ifdef CONFIG_BLOCK
+	case 'g':
+		return bdev_name(buf, end, ptr, spec, fmt);
+#endif
+
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {
@@ -1779,6 +1806,7 @@ qualifier:
  * %pF output the name of a function pointer with its offset
  * %pf output the name of a function pointer without its offset
  * %pB output the name of a backtrace symbol with its offset
+ * %pg output the name of a block_device
  * %pR output the address range in a struct resource with decoded flags
  * %pr output the address range in a struct resource with raw flags
  * %pb output the bitmap with field width as the number of bits
-- 
1.7.1