ext4: add debugging trigger for ext4_error()

Make it easy to test whether or not the error handling subsystem in
ext4 is working correctly.  This allows us to simulate an ext4_error()
by echoing a string to /sys/fs/ext4/<dev>/trigger_fs_error.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: ksumrall@google.com

1 files changed, 20 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 628cfcdc0823..9f1ae6b36502 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2473,6 +2473,23 @@ static ssize_t sbi_ui_store(struct ext4_attr *a,
         return count;
 }
 
+static ssize_t trigger_test_error(struct ext4_attr *a,
+                                  struct ext4_sb_info *sbi,
+                                  const char *buf, size_t count)
+{
+        int len = count;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        if (len && buf[len-1] == '\n')
+                len--;
+
+        if (len)
+                ext4_error(sbi->s_sb, "%.*s", len, buf);
+        return count;
+}
+
 #define EXT4_ATTR_OFFSET(_name,_mode,_show,_store,_elname) \
 static struct ext4_attr ext4_attr_##_name = {                   \
         .attr = {.name = __stringify(_name), .mode = _mode },   \
@@ -2503,6 +2520,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
 EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
 EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
 EXT4_RW_ATTR_SBI_UI(max_writeback_mb_bump, s_max_writeback_mb_bump);
+EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);
 
 static struct attribute *ext4_attrs[] = {
         ATTR_LIST(delayed_allocation_blocks),
@@ -2517,6 +2535,7 @@ static struct attribute *ext4_attrs[] = {
         ATTR_LIST(mb_stream_req),
         ATTR_LIST(mb_group_prealloc),
         ATTR_LIST(max_writeback_mb_bump),
+        ATTR_LIST(trigger_fs_error),
         NULL,
 };
 
@@ -3087,6 +3106,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                 goto out_free_orig;
         }
         sb->s_fs_info = sbi;
+        sbi->s_sb = sb;
         sbi->s_mount_opt = 0;
         sbi->s_resuid = EXT4_DEF_RESUID;
         sbi->s_resgid = EXT4_DEF_RESGID;