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

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Message-ID: <7a98e9c5-e0e5-9bf9-71b5-f75b9ddcdc4b@amazon.com>
Date:   Fri, 25 Feb 2022 18:09:59 +0100
From:   Alexander Graf <graf@...zon.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
CC:     <linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>, <ardb@...nel.org>,
        <dwmw@...zon.co.uk>
Subject: Re: [PATCH] ACPI: bus: Match first 9 bytes of device IDs

Hey Jason,

On 25.02.22 17:57, Jason A. Donenfeld wrote:
> Hi Alex,
>
> Thanks for this.
>
> I tested this out with the vmgenid driver, and I found a bug in this v1:
>
> On Fri, Feb 25, 2022 at 04:55:52PM +0100, Alexander Graf wrote:
>> -                             if (id->id[0] && !strcmp((char *)id->id, hwid->id))
>> +                             if (id->id[0] && !strncmp((char *)id->id, hwid->id, ACPI_ID_LEN))
> This only worked once I made that `ACPI_ID_LEN - 1`, because that length
> includes the null terminator. The below patch works fine. If you adjust
> that and send a quick v2 follow-up, I'm happy to ack it.
>
> Regards,
> Jason
>
> --------8<--------------------------
>
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 07f604832fd6..f179ebf16f21 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -829,7 +829,7 @@ static bool __acpi_match_device(struct acpi_device *device,
>                  /* First, check the ACPI/PNP IDs provided by the caller. */
>                  if (acpi_ids) {
>                          for (id = acpi_ids; id->id[0] || id->cls; id++) {
> -                               if (id->id[0] && !strcmp((char *)id->id, hwid->id))
> +                               if (id->id[0] && !strncmp((char *)id->id, hwid->id, ACPI_ID_LEN - 1))
>                                          goto out_acpi_match;
>                                  if (id->cls && __acpi_match_device_cls(id, hwid))
>                                          goto out_acpi_match;
> diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
> index b503c210c2d7..04751fc1d365 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_C", 0 }, /* Truncated "VM_Gen_Counter" */


You have to make this "VM_GEN_CO". I now match the full 9 bytes - unlike 
the previous patch I sent :)


Alex





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