Filesystem Class : Seek/Rewind

[deepikabhavnani]

dir_seek / dir_rewind functions at present do not return status. Mechanism should be provided to return error status.

ChanFS does not support directory seek/rewind functionality, and we cannot return -ENOSYS to indicate function not implemented.

Second best option is to assert in filesystem.

@geky @sg- Please suggest

[sg-]

why can't we return -ENOSYS ?

[deepikabhavnani]

API return type is void https://github.com/ARMmbed/mbed-os/blob/master/features/filesystem/FileSystem.h#L241

In order to return -ve value, we need to change API + all derived classes

[sg-]

Sounds like we know what to do then.

[geky]

Internally tracking IOTMORF-1677

Original definitions were taken from posix: http://pubs.opengroup.org/onlinepubs/7908799/xsh/rewinddir.html

Since then we've learned that not having the ability to return an error was a mistake. Returning error codes on all functions greatly simplifies things.

Unfortunately changing it now will break inheritance compatibility.

One option is to set a flag so that readdir returns an error on the next call.

I think just changing these definitions to return error codes would be better long run, but we should probably wait for the next release since filesystem things are currently moving around.