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Date: Sun, 1 Sep 2013 01:13:06 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Waiman Long <waiman.long@...com>, Ingo Molnar <mingo@...nel.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Jeff Layton <jlayton@...hat.com>,
Miklos Szeredi <mszeredi@...e.cz>,
Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Andi Kleen <andi@...stfloor.org>,
"Chandramouleeswaran, Aswin" <aswin@...com>,
"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
update of refcount
On Sun, Sep 01, 2013 at 12:27:58AM +0100, Al Viro wrote:
> On Sat, Aug 31, 2013 at 03:49:31PM -0700, Linus Torvalds wrote:
> > On Sat, Aug 31, 2013 at 2:23 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > >
> > > Hmm... OK, most of these suckers are actually doing just one component;
> > > we can look into 'print the ancestors as well' later, but the minimal
> > > variant would be something like this and it already covers a lot of those
> > > guys. Comments?
> >
> > Doesn't look wrong, but remember the /proc debugging thing? We
> > definitely wanted more than just one pathname component, and I don't
> > think that's completely rare.
> >
> > So I think it would be better to prepare for that, and simply print to
> > a local buffer, and then use the "string()" function on the end
> > result. Rather than do it directly from the dentry like you do, and
> > then having to do that widen() thing because you couldn't do the
> > strnlen() that that code wanted..
>
> Actually, right now I'm debugging a variant that avoids local buffers; use
> is %pD3 for grandparent/parent/name, etc., up to %pD4. %pd is equivalent
> to %pD1 (just the dentry name). Keep in mind that things like NFS use
> a _lot_ of what would be %pD2 in debugging printks and the string can grow
> fairly long, so I'd rather live with widen() than mess with local buffers
> here. I'll send an updated variant when I'm more or less satisfied with
> it...
Seems to be working... This doesn't include the metric arseload of
conversions in fs/*/* - just the sprintf part.
diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 3e8cb73..826147b 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -168,6 +168,17 @@ 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
+ %pD1
+ ...
+ %pD4
+
+ 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 (IOW, %pD1 is equivalent to %pd).
+
struct va_format:
%pV
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 739a3636..5db62bf 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 +533,88 @@ 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,
+ int depth)
+{
+ int i, n = 0;
+ const char *s;
+ char *p = buf;
+ const struct dentry *array[4];
+ char c;
+
+ if (depth < 0) {
+ depth = 1;
+ WARN_ON(1);
+ }
+ if (depth > 4) {
+ depth = 4;
+ WARN_ON(1);
+ }
+
+ rcu_read_lock();
+ for (i = 0; i < depth; i++) {
+ struct dentry *p = ACCESS_ONCE(d->d_parent);
+ array[i] = d;
+ if (d == p)
+ break;
+ d = p;
+ }
+ if (!i) { /* root dentry has a bloody inconvenient name */
+ i++;
+ goto do_name;
+ }
+ if (i == depth)
+ goto do_name;
+ while (i && n != spec.precision) {
+ if (buf < end)
+ *buf = '/';
+ buf++;
+ n++;
+do_name:
+ s = ACCESS_ONCE(array[--i]->d_name.name);
+ while (n != spec.precision && (c = *s++) != '\0') {
+ if (buf < end)
+ *buf = c;
+ buf++;
+ n++;
+ }
+ }
+ 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(p, 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 +1336,14 @@ 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, 1);
+ case 'D':
+ switch (fmt[1]) {
+ case '1': case '2': case '3': case '4':
+ return dentry_name(buf, end, ptr, spec, fmt[1] - '0');
+ }
+ break;
}
spec.flags |= SMALL;
if (spec.field_width == -1) {
--
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