linux-kernel - [PATCH v1 2/3] fs: allocate structure unconditionally in seq

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Message-Id: <14d8ee37ef4423dea354256598f22250fba3e7ab.1433193673.git.ydroneaud@opteya.com>
Date:	Mon,  1 Jun 2015 23:32:14 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Yann Droneaud <ydroneaud@...eya.com>
Subject: [PATCH v1 2/3] fs: allocate structure unconditionally in seq_open()

Since patch described below, from v2.6.15-rc1, seq_open()
could use a struct seq_file already allocated by the
caller if the pointer to the structure is stored in
file->private_data before calling the function.

    Commit 1abe77b0fc4b485927f1f798ae81a752677e1d05
    Author: Al Viro <viro@...iv.linux.org.uk>
    Date:   Mon Nov 7 17:15:34 2005 -0500

        [PATCH] allow callers of seq_open do allocation themselves

        Allow caller of seq_open() to kmalloc() seq_file + whatever else they
        want and set ->private_data to it.  seq_open() will then abstain from
        doing allocation itself.

As there's no more use for such feature, as it could
be easily replaced by calls to seq_open_private()
(see commit 39699037a5c9 ("[FS] seq_file: Introduce
the seq_open_private()")) and seq_release_private()
(see v2.6.0-test3), support for this uncommon feature
can be removed from seq_open().

Link: http://lkml.kernel.org/r/cover.1433193673.git.ydroneaud@opteya.com
Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
---
 fs/seq_file.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index c14f6a43beb5..a909f12dad4d 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -51,15 +51,16 @@ static void *seq_buf_alloc(unsigned long size)
  */
 int seq_open(struct file *file, const struct seq_operations *op)
 {
-	struct seq_file *p = file->private_data;
+	struct seq_file *p;
+
+	WARN_ON(file->private_data);
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
+	file->private_data = p;
 
-	if (!p) {
-		p = kmalloc(sizeof(*p), GFP_KERNEL);
-		if (!p)
-			return -ENOMEM;
-		file->private_data = p;
-	}
-	memset(p, 0, sizeof(*p));
 	mutex_init(&p->lock);
 	p->op = op;
 #ifdef CONFIG_USER_NS
-- 
2.4.2

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