ext4: Send notifications on error

Send a FS_ERROR message via fsnotify to a userspace monitoring tool
whenever a ext4 error condition is triggered. This follows the existing
error conditions in ext4, so it is hooked to the ext4_error* functions.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Gabriel Krisman Bertazi <[e-mail]>
Acked-by: Theodore Ts'o <[e-mail]>
Reviewed-by: Amir Goldstein <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/ext4/super.c

···
 #include <linux/part_stat.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/fsnotify.h>
 
 #include "ext4.h"
 #include "ext4_extents.h"	/* Needed for trace points definition */
···
 		       sb->s_id, function, line, current->comm, &vaf);
 		va_end(args);
 	}
+	fsnotify_sb_error(sb, NULL, error ? error : EFSCORRUPTED);
+
 	ext4_handle_error(sb, force_ro, error, 0, block, function, line);
 }
 
···
 			       current->comm, &vaf);
 		va_end(args);
 	}
+	fsnotify_sb_error(inode->i_sb, inode, error ? error : EFSCORRUPTED);
+
 	ext4_handle_error(inode->i_sb, false, error, inode->i_ino, block,
 			  function, line);
 }
···
 			       current->comm, path, &vaf);
 		va_end(args);
 	}
+	fsnotify_sb_error(inode->i_sb, inode, EFSCORRUPTED);
+
 	ext4_handle_error(inode->i_sb, false, EFSCORRUPTED, inode->i_ino, block,
 			  function, line);
 }
···
 		printk(KERN_CRIT "EXT4-fs error (device %s) in %s:%d: %s\n",
 		       sb->s_id, function, line, errstr);
 	}
+	fsnotify_sb_error(sb, NULL, errno ? errno : EFSCORRUPTED);
 
 	ext4_handle_error(sb, false, -errno, 0, 0, function, line);
 }