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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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