linux-kernel - Re: [PATCH] ACPI: bus: Match first 9 bytes of device IDs

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Message-ID: <YhkaAUQ/5ChlKlXt@zx2c4.com>
Date:   Fri, 25 Feb 2022 19:03:45 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Alexander Graf <graf@...zon.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>
Subject: Re: [PATCH] ACPI: bus: Match first 9 bytes of device IDs

On Fri, Feb 25, 2022 at 06:33:42PM +0100, Jason A. Donenfeld wrote:
> Either way is fine by me. Looking at all the current users of
> ACPI_ID_LEN, none of them really mind if it's >9. I can't see where
> it'd change any behavior or performance or really anything at all,
> anywhere. So I'm inclined to go with my original simpler solution. But
> again, either way is fine.
> 
> Alex, do you want to pick one of these and submit a v2 based on it? Or
> do you see a shortcoming in that approach?

I can confirm from testing that the below trivial diff fixes the issue.
I believe Ard is looking into the userspace/udev ramifications.

diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
index b503c210c2d7..4542ebb68ae0 100644
--- a/drivers/virt/vmgenid.c
+++ b/drivers/virt/vmgenid.c
@@ -78,8 +78,7 @@ static void vmgenid_acpi_notify(struct acpi_device *device, u32 event)
 }

 static const struct acpi_device_id vmgenid_ids[] = {
-	{ "QEMUVGID", 0 },	/* QEMU */
-	{ "VMGENID", 0 },	/* Firecracker */
+	{ "VM_GEN_COUNTER", 0 },
 	{ },
 };

diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 4bb71979a8fd..5da5d990ff58 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -211,7 +211,7 @@ struct css_device_id {
 	kernel_ulong_t driver_data;
 };

-#define ACPI_ID_LEN	9
+#define ACPI_ID_LEN	16

 struct acpi_device_id {
 	__u8 id[ACPI_ID_LEN];