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 and Pavel are proposing).

Signed-off-by: Cyrill Gorcunov <gorcu...@openvz.org>
CC: Pavel Emelyanov <xe...@parallels.com>
CC: Al Viro <v...@zeniv.linux.org.uk>
CC: Alexey Dobriyan <adobri...@gmail.com>
CC: Andrew Morton <a...@linux-foundation.org>
CC: James Bottomley <jbottom...@parallels.com>
CC: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
CC: Alexey Dobriyan <adobri...@gmail.com>
CC: Matthew Helsley <matt.hels...@gmail.com>
CC: "J. Bruce Fields" <bfie...@fieldses.org>
CC: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
---
 fs/proc/fd.c       |    2 ++
 include/linux/fs.h |    3 +++
 2 files changed, 5 insertions(+)

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
@@ -50,6 +50,8 @@ static int seq_show(struct seq_file *m,
        if (!ret) {
                 seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
                           (long long)file->f_pos, f_flags);
+               if (file->f_op->show_fdinfo)
+                       ret = file->f_op->show_fdinfo(m, file);
                fput(file);
        }
 
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
@@ -1517,6 +1517,8 @@ 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);
@@ -1545,6 +1547,7 @@ 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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