Date: Mon, 17 May 2021 16:27:49 -0400 From: Jung-uk Kim <junguk.kim@gmail.com> To: John Nielsen <lists@jnielsen.net>, "freebsd-acpi@freebsd.org" <freebsd-acpi@FreeBSD.org> Subject: Re: How to properly locate/parse ACPI table from kernel module? Message-ID: <6e1f13bd-dc8f-6b30-2b62-2841deea8781@gmail.com> In-Reply-To: <BCFCDCE9-F169-4C1C-AD0C-FDE511C0BC11@jnielsen.net> References: <BCFCDCE9-F169-4C1C-AD0C-FDE511C0BC11@jnielsen.net>
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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
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