proc: convert /proc/$PID/cmdline to seq_file interface

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

@@ -200,9 +200,16 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
 	return result;
 }
 
-static int proc_pid_cmdline(struct task_struct *task, char *buffer)
+static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
+			    struct pid *pid, struct task_struct *task)
 {
-	return get_cmdline(task, buffer, PAGE_SIZE);
+	/*
+	 * Rely on struct seq_operations::show() being called once
+	 * per internal buffer allocation. See single_open(), traverse().
+	 */
+	BUG_ON(m->size < PAGE_SIZE);
+	m->count += get_cmdline(task, m->buf, PAGE_SIZE);
+	return 0;
 }
 
 static int proc_pid_auxv(struct seq_file *m, struct pid_namespace *ns,
@@ -2567,7 +2574,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",    S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",    S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",    S_IRUGO, proc_pid_cmdline),
 	ONE("stat",       S_IRUGO, proc_tgid_stat),
 	ONE("statm",      S_IRUGO, proc_pid_statm),
 	REG("maps",       S_IRUGO, proc_pid_maps_operations),
@@ -2903,7 +2910,7 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	ONE("syscall",   S_IRUSR, proc_pid_syscall),
 #endif
-	INF("cmdline",   S_IRUGO, proc_pid_cmdline),
+	ONE("cmdline",   S_IRUGO, proc_pid_cmdline),
 	ONE("stat",      S_IRUGO, proc_tid_stat),
 	ONE("statm",     S_IRUGO, proc_pid_statm),
 	REG("maps",      S_IRUGO, proc_tid_maps_operations),