Revert "proc: revert /proc/uptime to ->read_proc hook"

This reverts commit 6c87df37.

proc files implemented through seq_file do pread(2) now.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

fs/proc/uptime.c

+#include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/proc_fs.h>
 #include <linux/sched.h>
+#include <linux/seq_file.h>
 #include <linux/time.h>
 #include <asm/cputime.h>
 
-static int proc_calc_metrics(char *page, char **start, off_t off,
-				 int count, int *eof, int len)
-{
-	if (len <= off + count)
-		*eof = 1;
-	*start = page + off;
-	len -= off;
-	if (len > count)
-		len = count;
-	if (len < 0)
-		len = 0;
-	return len;
-}
-
-static int uptime_read_proc(char *page, char **start, off_t off, int count,
-			    int *eof, void *data)
+static int uptime_proc_show(struct seq_file *m, void *v)
 {
 	struct timespec uptime;
 	struct timespec idle;
-	int len;
 	cputime_t idletime = cputime_add(init_task.utime, init_task.stime);
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	monotonic_to_bootbased(&uptime);
 	cputime_to_timespec(idletime, &idle);
-	len = sprintf(page, "%lu.%02lu %lu.%02lu\n",
+	seq_printf(m, "%lu.%02lu %lu.%02lu\n",
 			(unsigned long) uptime.tv_sec,
 			(uptime.tv_nsec / (NSEC_PER_SEC / 100)),
 			(unsigned long) idle.tv_sec,
 			(idle.tv_nsec / (NSEC_PER_SEC / 100)));
-	return proc_calc_metrics(page, start, off, count, eof, len);
+	return 0;
 }
 
+static int uptime_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, uptime_proc_show, NULL);
+}
+
+static const struct file_operations uptime_proc_fops = {
+	.open		= uptime_proc_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 static int __init proc_uptime_init(void)
 {
-	create_proc_read_entry("uptime", 0, NULL, uptime_read_proc, NULL);
+	proc_create("uptime", 0, NULL, &uptime_proc_fops);
 	return 0;
 }
 module_init(proc_uptime_init);