On 21. 5. 17., John Nielsen wrote:
> Hi all-
>
> I’m not much of a kernel programmer but I’m trying to maintain/improve the
> isboot module, which allows booting directly from iSCSI by reading the iSCSI
> Boot Firmware Table (iBFT), bringing up the interface with the details
> specified therein and connecting to the specified iSCSI target before trying
> to mount root.
>
> I’m not the original author but as the port maintainer I am hosting the code
> here: https://github.com/jnielsendotnet/isboot
>
> I have a test system where the module loads but fails to find the iBFT. I
> reviewed the iBFT code and realized it has a bunch of magic numbers mixed in
> with some random memory diving. If I’m reading it right (see
> https://github.com/jnielsendotnet/isboot/blob/master/src/ibft.h#L37 and
> https://github.com/jnielsendotnet/isboot/blob/master/src/ibft.c#L521), it
> looks like it scans all of the (kernel?) memory between 512K and 1M in
> 16-byte increments looking for one beginning with the string “iBFT”, which if
> it finds will be used as the offset for reading the table. I don’t know where
> the 512K and 1M values came from or if they are correct, but I do have a
> system where that method does not work.
>
> IIUC, the iBFT is an ACPI table, and it seems like using ACPI to find it
> would be safer and more reliable. So my question is: how does one do that?
> Are there other places in the kernel code that do this sort of thing that I
> could use as a model? Any gotchas I should know about as a (less-than) novice
> kernel programmer?
You may use AcpiGetTable() and AcpiPutTable(), e.g.,
status = AcpiGetTable(ACPI_SIG_IBFT, ...);
Jung-uk Kim
