How do I debug this FS error on a flash device?

Question

I have console access to an embedded linux device. This device has flash memory part of which is partitioned as a FAT filesystem.

Its running linux-2.6.31.

However I am seeing these errors on the console these days and the FAT file system becomes read only.

111109:154925 FAT: Filesystem error (dev loop0)
111109:154925 fat_get_cluster: invalid cluster chain (i_pos 0)
111109:154925 FAT: Filesystem error (dev loop0)
111109:154925 fat_get_cluster: invalid cluster chain (i_pos 0)

I cannot understand why this happened? What is the root cause? And what is the fix? I would appreciate answers that can point me how to investigate the possible root cause of this issue on the device.

Answer 1

The errors you are getting invalid cluster chain and filesystem error clearly shows that it is filesystem error.

Wikipedia entry on FAT says:

A partition is divided up into identically sized clusters, small blocks of contiguous space. Cluster sizes vary depending on the type of FAT file system being used and the size of the partition, typically cluster sizes lie somewhere between 2 kB and 32 kB. Each file may occupy one or more of these clusters depending on its size; thus, a file is represented by a chain of these clusters (referred to as a singly linked list). However these clusters are not necessarily stored adjacent to one another on the disk's surface but are often instead fragmented throughout the Data Region.

The File Allocation Table (FAT) is a list of entries that map to each cluster on the partition. Each entry records one of five things:

• the cluster number of the next cluster in a chain
• a special end of clusterchain (EOC) entry that indicates the end of a chain
• a special entry to mark a bad cluster
• a zero to note that the cluster is unused

This link says that somebody had solved similar problem with memory card using fsck.