procfs: Convert /proc/pid/fdinfo/ handling routines to seq-file v2

This patch converts /proc/pid/fdinfo/ handling routines to seq-file which
is needed to extend seq operations and plug in auxiliary fdinfo provides
from subsystems like eventfd/eventpoll/fsnotify.

Note the proc_fd_link no longer call for proc_fd_info, simply because
the guts of proc_fd_info() got merged into ->show() of that seq_file

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 64 insertions, 48 deletions

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 1b0f932b4bd9..9cef449c0f76 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -6,61 +6,68 @@
 #include <linux/namei.h>
 #include <linux/pid.h>
 #include <linux/security.h>
+#include <linux/file.h>
+#include <linux/seq_file.h>
 
 #include <linux/proc_fs.h>
 
 #include "internal.h"
 #include "fd.h"
 
-#define PROC_FDINFO_MAX 64
-
-static int proc_fd_info(struct inode *inode, struct path *path, char *info)
+static int seq_show(struct seq_file *m, void *v)
 {
-        struct task_struct *task = get_proc_task(inode);
         struct files_struct *files = NULL;
-        int fd = proc_fd(inode);
-        struct file *file;
+        int f_flags = 0, ret = -ENOENT;
+        struct file *file = NULL;
+        struct task_struct *task;
+
+        task = get_proc_task(m->private);
+        if (!task)
+                return -ENOENT;
+
+        files = get_files_struct(task);
+        put_task_struct(task);
 
-        if (task) {
-                files = get_files_struct(task);
-                put_task_struct(task);
-        }
         if (files) {
-                /*
-                 * We are not taking a ref to the file structure, so we must
-                 * hold ->file_lock.
-                 */
+                int fd = proc_fd(m->private);
+
                 spin_lock(&files->file_lock);
                 file = fcheck_files(files, fd);
                 if (file) {
-                        unsigned int f_flags;
-                        struct fdtable *fdt;
+                        struct fdtable *fdt = files_fdtable(files);
 
-                        fdt = files_fdtable(files);
                         f_flags = file->f_flags & ~O_CLOEXEC;
                         if (close_on_exec(fd, fdt))
                                 f_flags |= O_CLOEXEC;
 
-                        if (path) {
-                                *path = file->f_path;
-                                path_get(&file->f_path);
-                        }
-                        if (info)
-                                snprintf(info, PROC_FDINFO_MAX,
-                                         "pos:\t%lli\n"
-                                         "flags:\t0%o\n",
-                                         (long long) file->f_pos,
-                                         f_flags);
-                        spin_unlock(&files->file_lock);
-                        put_files_struct(files);
-                        return 0;
+                        get_file(file);
+                        ret = 0;
                 }
                 spin_unlock(&files->file_lock);
                 put_files_struct(files);
         }
-        return -ENOENT;
+
+        if (!ret) {
+                seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
+                           (long long)file->f_pos, f_flags);
+                fput(file);
+        }
+
+        return ret;
 }
 
+static int seq_fdinfo_open(struct inode *inode, struct file *file)
+{
+        return single_open(file, seq_show, inode);
+}
+
+static const struct file_operations proc_fdinfo_file_operations = {
+        .open           = seq_fdinfo_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = single_release,
+};
+
 static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
 {
         struct files_struct *files;
@@ -130,7 +137,32 @@ static const struct dentry_operations tid_fd_dentry_operations = {
 
 static int proc_fd_link(struct dentry *dentry, struct path *path)
 {
-        return proc_fd_info(dentry->d_inode, path, NULL);
+        struct files_struct *files = NULL;
+        struct task_struct *task;
+        int ret = -ENOENT;
+
+        task = get_proc_task(dentry->d_inode);
+        if (task) {
+                files = get_files_struct(task);
+                put_task_struct(task);
+        }
+
+        if (files) {
+                int fd = proc_fd(dentry->d_inode);
+                struct file *fd_file;
+
+                spin_lock(&files->file_lock);
+                fd_file = fcheck_files(files, fd);
+                if (fd_file) {
+                        *path = fd_file->f_path;
+                        path_get(&fd_file->f_path);
+                        ret = 0;
+                }
+                spin_unlock(&files->file_lock);
+                put_files_struct(files);
+        }
+
+        return ret;
 }
 
 static struct dentry *
@@ -245,22 +277,6 @@ out_no_task:
         return retval;
 }
 
-static ssize_t proc_fdinfo_read(struct file *file, char __user *buf,
-                                size_t len, loff_t *ppos)
-{
-        char tmp[PROC_FDINFO_MAX];
-        int err = proc_fd_info(file->f_path.dentry->d_inode, NULL, tmp);
-        if (!err)
-                err = simple_read_from_buffer(buf, len, ppos, tmp, strlen(tmp));
-        return err;
-}
-
-static const struct file_operations proc_fdinfo_file_operations = {
-        .open           = nonseekable_open,
-        .read           = proc_fdinfo_read,
-        .llseek         = no_llseek,
-};
-
 static int proc_readfd(struct file *filp, void *dirent, filldir_t filldir)
 {
         return proc_readfd_common(filp, dirent, filldir, proc_fd_instantiate);