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Subject[patch 3/8] procfs: Add ability to plug in auxiliary fdinfo providers
This patch brings ability to print out auxiliary data associated
with file in procfs interface /proc/pid/fdinfo/fd.

In particular further patches make eventfd, evenpoll, signalfd
and fsnotify to print additional information complete enough
to restore these objects after checkpoint.

To simplify the code we add show_fdinfo callback inside
struct file_operations (as Al proposed and Pavel are proposing).

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Pavel Emelyanov <xemul@parallels.com>
CC: Al Viro <viro@ZenIV.linux.org.uk>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: James Bottomley <jbottomley@parallels.com>
---
fs/proc/fd.c | 51 ++++++++++++++++++++++++++++++++++++---------------
include/linux/fs.h | 3 +++
2 files changed, 39 insertions(+), 15 deletions(-)

Index: linux-2.6.git/fs/proc/fd.c
===================================================================
--- linux-2.6.git.orig/fs/proc/fd.c
+++ linux-2.6.git/fs/proc/fd.c
@@ -15,11 +15,11 @@
#include "fd.h"

struct proc_fdinfo {
- loff_t f_pos;
- int f_flags;
+ struct file *f_file;
+ int f_flags;
};

-static int fdinfo_open_helper(struct inode *inode, int *f_flags, struct path *path)
+static int fdinfo_open_helper(struct inode *inode, int *f_flags, struct file **f_file, struct path *path)
{
struct files_struct *files = NULL;
struct task_struct *task;
@@ -49,6 +49,10 @@ static int fdinfo_open_helper(struct ino
*path = fd_file->f_path;
path_get(&fd_file->f_path);
}
+ if (f_file) {
+ *f_file = fd_file;
+ get_file(fd_file);
+ }
ret = 0;
}
spin_unlock(&files->file_lock);
@@ -61,28 +65,44 @@ static int fdinfo_open_helper(struct ino
static int seq_show(struct seq_file *m, void *v)
{
struct proc_fdinfo *fdinfo = m->private;
- seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
- (long long)fdinfo->f_pos,
- fdinfo->f_flags);
- return 0;
+ int ret;
+
+ ret = seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
+ (long long)fdinfo->f_file->f_pos,
+ fdinfo->f_flags);
+
+ if (!ret && fdinfo->f_file->f_op->show_fdinfo)
+ ret = fdinfo->f_file->f_op->show_fdinfo(m, fdinfo->f_file);
+
+ return ret;
}

static int seq_fdinfo_open(struct inode *inode, struct file *file)
{
- struct proc_fdinfo *fdinfo = NULL;
- int ret = -ENOENT;
+ struct proc_fdinfo *fdinfo;
+ struct seq_file *m;
+ int ret;

fdinfo = kzalloc(sizeof(*fdinfo), GFP_KERNEL);
if (!fdinfo)
return -ENOMEM;

- ret = fdinfo_open_helper(inode, &fdinfo->f_flags, NULL);
- if (!ret) {
- ret = single_open(file, seq_show, fdinfo);
- if (!ret)
- fdinfo = NULL;
+ ret = fdinfo_open_helper(inode, &fdinfo->f_flags, &fdinfo->f_file, NULL);
+ if (ret)
+ goto err_free;
+
+ ret = single_open(file, seq_show, fdinfo);
+ if (ret) {
+ put_filp(fdinfo->f_file);
+ goto err_free;
}

+ m = file->private_data;
+ m->private = fdinfo;
+
+ return ret;
+
+err_free:
kfree(fdinfo);
return ret;
}
@@ -92,6 +112,7 @@ static int seq_fdinfo_release(struct ino
struct seq_file *m = file->private_data;
struct proc_fdinfo *fdinfo = m->private;

+ put_filp(fdinfo->f_file);
kfree(fdinfo);

return single_release(inode, file);
@@ -173,7 +194,7 @@ static const struct dentry_operations ti

static int proc_fd_link(struct dentry *dentry, struct path *path)
{
- return fdinfo_open_helper(dentry->d_inode, NULL, path);
+ return fdinfo_open_helper(dentry->d_inode, NULL, NULL, path);
}

static struct dentry *
Index: linux-2.6.git/include/linux/fs.h
===================================================================
--- linux-2.6.git.orig/include/linux/fs.h
+++ linux-2.6.git/include/linux/fs.h
@@ -1775,6 +1775,8 @@ struct block_device_operations;
#define HAVE_COMPAT_IOCTL 1
#define HAVE_UNLOCKED_IOCTL 1

+struct seq_file;
+
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
@@ -1803,6 +1805,7 @@ struct file_operations {
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
+ int (*show_fdinfo)(struct seq_file *m, struct file *f);
};

struct inode_operations {


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