Hi,
Please find a revised patchset to remove support for
passing pre-allocated struct seq_file to seq_open().
Such feature is undocumented and prone to error.
In particular, if seq_release() is used in release
handler, it will kfree() a pointer which was not
allocated by seq_open().
So, please find a patchset that drop the support for
pre-allocated struct seq_file: it's only of use in
proc_namespace.c and can be easily replaced by using
seq_open_private()/seq_release_private().
Additionally, it documents the use of file->private_data
to hold pointer to struct seq_file by seq_open().
Changes from v0 [0]:
- convert kmalloc() + memset() to kzalloc()
- revised a bit commit messages
[0] [PATCH 0/3] seq_file allocation in seq_open()
http://lkml.kernel.org/r/[email protected]
http://lkml.kernel.org/g/[email protected]
Yann Droneaud (3):
fs: use seq_open_private() for proc_mounts
fs: allocate structure unconditionally in seq_open()
fs: documents seq_open()'s usage of file->private_data
fs/mount.h | 3 ---
fs/namespace.c | 6 +++---
fs/proc_namespace.c | 34 ++++++++++++++++------------------
fs/seq_file.c | 19 +++++++++++--------
4 files changed, 30 insertions(+), 32 deletions(-)
--
2.4.2
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 <[email protected]>
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.
Such behavior is only used by mounts_open_common().
In order to drop support for such uncommon feature,
proc_mounts is converted to use seq_open_private(),
which take care of allocating the proc_mounts structure,
making it available through ->private in struct seq_file.
Conversely, proc_mounts is converted to use seq_release_private(),
in order to release the private structure allocated by
seq_open_private().
Then, ->private is used directly instead of proc_mounts()
macro to access to the proc_mounts structure.
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yann Droneaud <[email protected]>
---
fs/mount.h | 3 ---
fs/namespace.c | 6 +++---
fs/proc_namespace.c | 34 ++++++++++++++++------------------
3 files changed, 19 insertions(+), 24 deletions(-)
diff --git a/fs/mount.h b/fs/mount.h
index b5b8082bfa42..14db05d424f7 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -118,7 +118,6 @@ static inline void unlock_mount_hash(void)
}
struct proc_mounts {
- struct seq_file m;
struct mnt_namespace *ns;
struct path root;
int (*show)(struct seq_file *, struct vfsmount *);
@@ -127,8 +126,6 @@ struct proc_mounts {
loff_t cached_index;
};
-#define proc_mounts(p) (container_of((p), struct proc_mounts, m))
-
extern const struct seq_operations mounts_op;
extern bool __is_local_mountpoint(struct dentry *dentry);
diff --git a/fs/namespace.c b/fs/namespace.c
index f30c78a2b878..ecc277107e93 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1226,7 +1226,7 @@ EXPORT_SYMBOL(replace_mount_options);
/* iterator; we want it to have access to namespace_sem, thus here... */
static void *m_start(struct seq_file *m, loff_t *pos)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
down_read(&namespace_sem);
if (p->cached_event == p->ns->event) {
@@ -1247,7 +1247,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
p->cached_mount = seq_list_next(v, &p->ns->list, pos);
p->cached_index = *pos;
@@ -1261,7 +1261,7 @@ static void m_stop(struct seq_file *m, void *v)
static int m_show(struct seq_file *m, void *v)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
struct mount *r = list_entry(v, struct mount, mnt_list);
return p->show(m, &r->mnt);
}
diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 8db932da4009..8ebd9a334085 100644
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -17,7 +17,8 @@
static unsigned mounts_poll(struct file *file, poll_table *wait)
{
- struct proc_mounts *p = proc_mounts(file->private_data);
+ struct seq_file *m = file->private_data;
+ struct proc_mounts *p = m->private;
struct mnt_namespace *ns = p->ns;
unsigned res = POLLIN | POLLRDNORM;
int event;
@@ -25,8 +26,8 @@ static unsigned mounts_poll(struct file *file, poll_table *wait)
poll_wait(file, &p->ns->poll, wait);
event = ACCESS_ONCE(ns->event);
- if (p->m.poll_event != event) {
- p->m.poll_event = event;
+ if (m->poll_event != event) {
+ m->poll_event = event;
res |= POLLERR | POLLPRI;
}
@@ -92,7 +93,7 @@ static void show_type(struct seq_file *m, struct super_block *sb)
static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
struct mount *r = real_mount(mnt);
int err = 0;
struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
@@ -126,7 +127,7 @@ out:
static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
struct mount *r = real_mount(mnt);
struct super_block *sb = mnt->mnt_sb;
struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
@@ -186,7 +187,7 @@ out:
static int show_vfsstat(struct seq_file *m, struct vfsmount *mnt)
{
- struct proc_mounts *p = proc_mounts(m);
+ struct proc_mounts *p = m->private;
struct mount *r = real_mount(mnt);
struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
struct super_block *sb = mnt_path.dentry->d_sb;
@@ -236,6 +237,7 @@ static int mounts_open_common(struct inode *inode, struct file *file,
struct mnt_namespace *ns = NULL;
struct path root;
struct proc_mounts *p;
+ struct seq_file *m;
int ret = -EINVAL;
if (!task)
@@ -260,26 +262,21 @@ static int mounts_open_common(struct inode *inode, struct file *file,
task_unlock(task);
put_task_struct(task);
- ret = -ENOMEM;
- p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
- if (!p)
+ ret = seq_open_private(file, &mounts_op, sizeof(struct proc_mounts));
+ if (ret)
goto err_put_path;
- file->private_data = &p->m;
- ret = seq_open(file, &mounts_op);
- if (ret)
- goto err_free;
+ m = file->private_data;
+ m->poll_event = ns->event;
+ p = m->private;
p->ns = ns;
p->root = root;
- p->m.poll_event = ns->event;
p->show = show;
p->cached_event = ~0ULL;
return 0;
- err_free:
- kfree(p);
err_put_path:
path_put(&root);
err_put_ns:
@@ -290,10 +287,11 @@ static int mounts_open_common(struct inode *inode, struct file *file,
static int mounts_release(struct inode *inode, struct file *file)
{
- struct proc_mounts *p = proc_mounts(file->private_data);
+ struct seq_file *m = file->private_data;
+ struct proc_mounts *p = m->private;
path_put(&p->root);
put_mnt_ns(p->ns);
- return seq_release(inode, file);
+ return seq_release_private(inode, file);
}
static int mounts_open(struct inode *inode, struct file *file)
--
2.4.2
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 <[email protected]>
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/[email protected]
Signed-off-by: Yann Droneaud <[email protected]>
---
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
seq_open() store its struct seq_file in file->private_data,
thus, it must not be modified by user of seq_file.
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yann Droneaud <[email protected]>
---
fs/seq_file.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/seq_file.c b/fs/seq_file.c
index a909f12dad4d..e48ef5682bfa 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -48,6 +48,8 @@ static void *seq_buf_alloc(unsigned long size)
* ERR_PTR(error). In the end of sequence they return %NULL. ->show()
* returns 0 in case of success and negative number in case of error.
* Returning SEQ_SKIP means "discard this element and move on".
+ * Note: seq_open() will allocate a struct seq_file and store its
+ * pointer in @file->private_data. This pointer should not be modified.
*/
int seq_open(struct file *file, const struct seq_operations *op)
{
--
2.4.2