Re: [PATCH] scsi_debug: rework resp_report_luns

[Douglas Gilbert <dgilbert@interlog.com>]

On 15-02-24 04:37 PM, Tomas Winkler wrote:
> 1. Fix the error check: the alloc length should be > 16
> and not > 4

You are proposing to make a marginally incorrect test
completely incorrect!

The governing rule for almost all "allocation length" fields
in SCSI commands (that return data-in) is:

"An allocation length of zero specifies that no data shall
be transferred. This condition shall not be considered an
error." [in section 4.2.5.6 of spc5r03.pdf and REPORT LUNS
refers to this]

If the REPORT LUNS allocation length is less that 4 then
the caller doesn't even get the response length back so that
has no practical use IMO. If allocation_length=0 and the SCSI
status is GOOD then all that tells you is that REPORT LUNS is
supported, but it has been a mandatory command for 10 years
so that is to be expected.

> 2. Remove duplicated boundary checks which simplify
> the fill-in loop
> 3. Use more of scsi generic API

Something else you might fix is the stack allocation of
2048+8 bytes:
    u8 arr[SDEBUG_RLUN_ARR_SZ];

It would be better to work out how many LUs the
parent target has and use kmalloc() (or friend)
to make a response buffer large enough. And
"large enough" needs to be no larger than the
allocation_length indicates however that requires
extra care in the loop stopping conditions.

Doug Gilbert