Enhance the WAL file related error

[ahrtr]

This PR should be helpful to debug #14252

The ErrFileNotFound was used for for three cases:

1. There is no any WAL files (probably due to no read permission);
2. There is no WAL files matching the snapshot index;
3. The WAL file seqs do not increase continuously.

It's not good for debug when users see the ErrFileNotFound error,
so in this PR, a different error is returned for each case above.

Signed-off-by: Benjamin Wang wachao@vmware.com

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[ahrtr]

cc @spzala @ptabor

[spzala]

@ahrtr thanks, this can be very helpful with debugging. I don't see anything rely on the return err, ErrFileNotFound but to be on safe side, probably good idea to update CHANGELOG around error enhancement? (e.g. Verify() in the wal.go will return different error with these changes) Thanks!

[ahrtr]

probably good idea to update CHANGELOG around error enhancement? (e.g. Verify() in the wal.go will return different error with these changes)

Thanks @spzala for the comment. I thought about updating the CHANGELOG, but didn't do it, reasons:

1. We do not have detailed document on WAL, so nobody will understand the CHANGELOG item without digging into the source code;
2. The change is a very minor change and just to enhance the error message, which is only useful for debugging related issue.

So I'd like not to update the CHANGELOG, what do you think?

[spzala]

probably good idea to update CHANGELOG around error enhancement? (e.g. Verify() in the wal.go will return different error with these changes)

Thanks @spzala for the comment. I thought about updating the CHANGELOG, but didn't do it, reasons:

1. We do not have detailed document on WAL, so nobody will understand the CHANGELOG item without digging into the source code;

2. The change is a very minor change and just to enhance the error message, which is only useful for debugging related issue.

So I'd like not to update the CHANGELOG, what do you think?

@ahrtr ok, that's fair. It's minor as you said and I don't have a hard opinion.