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From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jia He <justin.he@arm.com>, 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>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ira Weiny <ira.weiny@intel.com>,
	Eric Biggers <ebiggers@google.com>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: [PATCH 03/14] d_path: regularize handling of root dentry in __dentry_path()
Date: Wed, 19 May 2021 00:48:50 +0000	[thread overview]
Message-ID: <20210519004901.3829541-3-viro@zeniv.linux.org.uk> (raw)
In-Reply-To: <20210519004901.3829541-1-viro@zeniv.linux.org.uk>

All path-forming primitives boil down to sequence of prepend_name()
on dentries encountered along the way toward root.  Each time we prepend
/ + dentry name to the buffer.  Normally that does exactly what we want,
but there's a corner case when we don't call prepend_name() at all (in case
of __dentry_path() that happens if we are given root dentry).  We obviously
want to end up with "/", rather than "", so this corner case needs to be
handled.

__dentry_path() used to manually put '/' in the end of buffer before
doing anything else, to be overwritten by the first call of prepend_name()
if one happens and to be left in place if we don't call prepend_name() at
all.  That required manually checking that we had space in the buffer
(prepend_name() and prepend() take care of such checks themselves) and lead
to clumsy keeping track of return value.

A better approach is to check if the main loop has added anything
into the buffer and prepend "/" if it hasn't.  A side benefit of using prepend()
is that it does the right thing if we'd already run out of buffer, making
the overflow-handling logics simpler.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/d_path.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/fs/d_path.c b/fs/d_path.c
index 1a1cf05e7780..b3324ae7cfe2 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c
@@ -329,31 +329,22 @@ char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
 static char *__dentry_path(const struct dentry *d, char *p, int buflen)
 {
 	const struct dentry *dentry;
-	char *end, *retval;
+	char *end;
 	int len, seq = 0;
-	int error = 0;
-
-	if (buflen < 1)
-		goto Elong;
 
 	rcu_read_lock();
 restart:
 	dentry = d;
 	end = p;
 	len = buflen;
-	/* Get '/' right */
-	retval = end-1;
-	*retval = '/';
 	read_seqbegin_or_lock(&rename_lock, &seq);
 	while (!IS_ROOT(dentry)) {
 		const struct dentry *parent = dentry->d_parent;
 
 		prefetch(parent);
-		error = prepend_name(&end, &len, &dentry->d_name);
-		if (error)
+		if (unlikely(prepend_name(&end, &len, &dentry->d_name) < 0))
 			break;
 
-		retval = end;
 		dentry = parent;
 	}
 	if (!(seq & 1))
@@ -363,11 +354,9 @@ static char *__dentry_path(const struct dentry *d, char *p, int buflen)
 		goto restart;
 	}
 	done_seqretry(&rename_lock, seq);
-	if (error)
-		goto Elong;
-	return retval;
-Elong:
-	return ERR_PTR(-ENAMETOOLONG);
+	if (len == buflen)
+		prepend(&end, &len, "/", 1);
+	return len >= 0 ? end : ERR_PTR(-ENAMETOOLONG);
 }
 
 char *dentry_path_raw(const struct dentry *dentry, char *buf, int buflen)
-- 
2.11.0


  parent reply	other threads:[~2021-05-19  0:51 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-08 12:25 [PATCH RFC 0/3] make '%pD' print full path for file Jia He
2021-05-08 12:25 ` [PATCH RFC 1/3] fs: introduce helper d_path_fast() Jia He
2021-05-08 15:30   ` Linus Torvalds
2021-05-08 19:13     ` Al Viro
2021-05-08 20:39       ` Linus Torvalds
2021-05-08 21:05         ` Al Viro
2021-05-08 22:17           ` Linus Torvalds
2021-05-08 22:46             ` Al Viro
2021-05-08 22:48               ` Linus Torvalds
2021-05-08 23:15               ` Al Viro
2021-05-08 23:18                 ` Al Viro
2021-05-09 22:58                 ` Eric W. Biederman
2021-05-10 12:51                   ` Christian Brauner
2021-05-10  7:20                 ` Christian Brauner
2021-05-08 22:42           ` Linus Torvalds
2021-05-08 22:47             ` Linus Torvalds
2021-05-09  2:28               ` Al Viro
2021-05-09  2:53                 ` Linus Torvalds
2021-05-19  0:43                   ` [PATCHSET] d_path cleanups Al Viro
2021-05-19  0:48                     ` [PATCH 01/14] d_path: "\0" is {0,0}, not {0} Al Viro
2021-05-19  0:48                       ` [PATCH 02/14] d_path: saner calling conventions for __dentry_path() Al Viro
2021-06-25  9:32                         ` Justin He
2021-07-07  4:52                           ` Justin He
2021-05-19  0:48                       ` Al Viro [this message]
2021-07-07  4:50                         ` [PATCH 03/14] d_path: regularize handling of root dentry in __dentry_path() Justin He
2021-05-19  0:48                       ` [PATCH 04/14] d_path: get rid of path_with_deleted() Al Viro
2021-05-19  0:48                       ` [PATCH 05/14] getcwd(2): saner logics around prepend_path() call Al Viro
2021-07-07  7:41                         ` Justin He
2021-05-19  0:48                       ` [PATCH 06/14] d_path: don't bother with return value of prepend() Al Viro
2021-06-24  6:13                         ` Justin He
2021-05-19  0:48                       ` [PATCH 07/14] d_path: lift -ENAMETOOLONG handling into callers of prepend_path() Al Viro
2021-06-25  9:18                         ` Justin He
2021-06-28  5:20                           ` Justin He
2021-05-19  0:48                       ` [PATCH 08/14] d_path: make prepend_name() boolean Al Viro
2021-05-20  9:12                         ` Justin He
2021-05-20  9:19                           ` Andy Shevchenko
2021-05-20 14:53                           ` Petr Mladek
2021-05-20 19:35                             ` Al Viro
2021-07-07  7:43                         ` Justin He
2021-05-19  0:48                       ` [PATCH 09/14] d_path: introduce struct prepend_buffer Al Viro
2021-06-23 13:28                         ` Justin He
2021-06-24  9:29                           ` Enrico Weigelt, metux IT consult
2021-06-25  0:43                             ` Justin He
2021-06-28 16:42                               ` Enrico Weigelt, metux IT consult
2021-06-28 17:10                                 ` Andy Shevchenko
2021-05-19  0:48                       ` [PATCH 10/14] d_path: prepend_path(): get rid of vfsmnt Al Viro
2021-05-19  0:48                       ` [PATCH 11/14] d_path: prepend_path(): lift resetting b in case when we'd return 3 out of loop Al Viro
2021-05-19  0:48                       ` [PATCH 12/14] d_path: prepend_path(): lift the inner loop into a new helper Al Viro
2021-05-19  8:07                         ` Andy Shevchenko
2021-05-19 15:55                           ` Al Viro
2021-07-07  7:52                         ` Justin He
2021-05-19  0:49                       ` [PATCH 13/14] d_path: prepend_path() is unlikely to return non-zero Al Viro
2021-06-25  8:00                         ` Justin He
2021-06-25 17:58                           ` Al Viro
2021-06-28  3:28                             ` Justin He
2021-06-28  4:14                               ` Al Viro
2021-06-28  4:36                                 ` Justin He
2021-06-28  4:37                         ` Justin He
2021-05-19  0:49                       ` [PATCH 14/14] getcwd(2): clean up error handling Al Viro
2021-07-07  8:03                         ` Justin He
2021-06-24  6:05                       ` [PATCH 01/14] d_path: "\0" is {0,0}, not {0} Justin He
2021-05-19  2:39                     ` [PATCHSET] d_path cleanups Linus Torvalds
2021-06-22 14:00                     ` Justin He
2021-05-09  2:20         ` [PATCH RFC 1/3] fs: introduce helper d_path_fast() Al Viro
2021-05-09  4:58           ` Al Viro
2021-05-10 16:16           ` Eric W. Biederman
2021-05-10 15:07         ` Justin He
2021-05-10 17:03           ` Linus Torvalds
2021-05-08 12:25 ` [PATCH RFC 2/3] lib/vsprintf.c: make %pD print full path for file Jia He
2021-05-10  3:46   ` Sergey Senozhatsky
2021-05-10 13:04   ` Petr Mladek
2021-05-10 14:25     ` Justin He
2021-05-27  7:20     ` Justin He
2021-05-27  9:14       ` Petr Mladek
2021-05-08 12:25 ` [PATCH RFC 3/3] s390/hmcdrv: remove the redundant directory path in debug message Jia He

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