staging/lustre/llite: move root_squash from sysfs to debugfs

root_squash control got accidentally moved to sysfs instead of
debugfs, and the write side of it was also broken expecting a
userspace buffer.
It contains both uid and gid values in a single file, so debugfs
is a clear place for it.
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Fixes: c948390f "fix inconsistencies of root squash feature"
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/lproc_llite.c

@@ -924,27 +924,29 @@ static ssize_t ll_unstable_stats_seq_write(struct file *file,
 }
 LPROC_SEQ_FOPS(ll_unstable_stats);
 
-static ssize_t root_squash_show(struct kobject *kobj, struct attribute *attr,
-				char *buf)
+static int ll_root_squash_seq_show(struct seq_file *m, void *v)
 {
-	struct ll_sb_info *sbi = container_of(kobj, struct ll_sb_info,
-					      ll_kobj);
+	struct super_block *sb = m->private;
+	struct ll_sb_info *sbi = ll_s2sbi(sb);
 	struct root_squash_info *squash = &sbi->ll_squash;
 
-	return sprintf(buf, "%u:%u\n", squash->rsi_uid, squash->rsi_gid);
+	seq_printf(m, "%u:%u\n", squash->rsi_uid, squash->rsi_gid);
+	return 0;
 }
 
-static ssize_t root_squash_store(struct kobject *kobj, struct attribute *attr,
-				 const char *buffer, size_t count)
+static ssize_t ll_root_squash_seq_write(struct file *file,
+					const char __user *buffer,
+					size_t count, loff_t *off)
 {
-	struct ll_sb_info *sbi = container_of(kobj, struct ll_sb_info,
-					      ll_kobj);
+	struct seq_file *m = file->private_data;
+	struct super_block *sb = m->private;
+	struct ll_sb_info *sbi = ll_s2sbi(sb);
 	struct root_squash_info *squash = &sbi->ll_squash;
 
 	return lprocfs_wr_root_squash(buffer, count, squash,
-				      ll_get_fsname(sbi->ll_sb, NULL, 0));
+				      ll_get_fsname(sb, NULL, 0));
 }
-LUSTRE_RW_ATTR(root_squash);
+LPROC_SEQ_FOPS(ll_root_squash);
 
 static int ll_nosquash_nids_seq_show(struct seq_file *m, void *v)
 {
@@ -997,6 +999,8 @@ static struct lprocfs_vars lprocfs_llite_obd_vars[] = {
 	{ "statahead_stats",  &ll_statahead_stats_fops, NULL, 0 },
 	{ "unstable_stats",   &ll_unstable_stats_fops, NULL },
 	{ "sbi_flags",	      &ll_sbi_flags_fops, NULL, 0 },
+	{ .name =       "root_squash",
+	  .fops =       &ll_root_squash_fops			},
 	{ .name =		"nosquash_nids",
 	  .fops =		&ll_nosquash_nids_fops		},
 	{ NULL }
@@ -1027,7 +1031,6 @@ static struct attribute *llite_attrs[] = {
 	&lustre_attr_max_easize.attr,
 	&lustre_attr_default_easize.attr,
 	&lustre_attr_xattr_cache.attr,
-	&lustre_attr_root_squash.attr,
 	NULL,
 };