Bug Report: MFS File Open fails for append when file size = cluster size

[chrissolomon]

Hi,

Still working on getting MQX 4.1.1 on a K70 stable enough for for an update to our product. 6 weeks and counting.

My CTO wants me to ask if you guys have heard of unit tests. There cool. Give them a look on wikipedia.

Anyway, here's the bug:

We have found that when a file is exactly a multiple of the cluster size (in our case 4096 bytes) opening with filemode a or a+ fails (fopen returns null).

Looking through the code it seems that MFS_Move_file_pointer returns sets the error_code to MFS_EOF.

It seems that when the data ends exactly at the end of a cluster, MFS_get_cluster_from_fat returns CLUSTER_EOF as the new "current_cluster".

This sets the error_code to MFS_EOF, which doesn't seem unreasonable since we are seeking to the end of the file, however when we get back to _io_mfs_open, it sees this error and fails.

I *think* a simple fix is to check if the error_code is

if( error_code == MFS_EOF ) {
     error_code = MFS_NO_ERROR;
}

at line 462 of mfs_init.c (or thereabouts), but I am not an expert on FAT file systems, so I'm looking for confirmation?

Thanks

Chris

P.S.

Easy to replicate, just use the sh_write test app.

[ironsean]

Wouldn't it make more sense to change the code that finds Cluster_EOF to simply not throw an MFS_EOF instead? Have you had any issues with that change?

[chrissolomon]

Sorry for the late reply, been off the forums for a while. We have been using this for a few months now, in production, with no issues

[RadekS]

Hi Chris,

thank you for confirmation.

Just for make it sure. Did you use fix from your initial topic (edit mfs_init.c) or recommended solution with use r+/w/w+ modes instead of append mode?

Anyway, current MFS in MQX 4.2 was reworked and do not suffer this by this bug.

Have a great day,
RadekS

[ironsean]

I can confirm I've been using the edit mfs_init.c solution since January without issue. Now that MQX 4.2 is out and should have the issue resolved I will try that, if I can get past the printf linking issue I've been getting with my code in MQX 4.2.

[juarez]

Hi Chris Solomon

I'm having this problem. I would like know if your solution solved the problem without side effect.

Thanks.

[RadekS]

Thank you for your bug report.

Yes, you are right. It is known issue. Unfortunately, append mode is implemented wrongly.

As workaround, please use r+/w/w+ modes instead of append mode and seeks manually according your needs.

Next MQX release will contain complete redesigned MFS subsystem which will solve this issue.

Have a great day,
RadekS

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