acpi: add function to extract oem_id and oem_table_id from the user's SLIC

The acpi_get_slic_oem() function stores pointers to these fields in the
(first) SLIC table that the user passes in with the -acpitable switch.

Cc: "Michael S. Tsirkin" <mst@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Igor Mammedov <imammedo@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Richard W.M. Jones <rjones@redhat.com>
Cc: Aleksei Kovura <alex3kov@zoho.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Cc: Steven Newbury <steve@snewbury.org.uk>
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1248758
LP: https://bugs.launchpad.net/qemu/+bug/1533848Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NSteven Newbury <steve@snewbury.org.uk>

hw/acpi/core.c

@@ -350,6 +350,22 @@ uint8_t *acpi_table_next(uint8_t *current)
     }
 }
 
+int acpi_get_slic_oem(AcpiSlicOem *oem)
+{
+    uint8_t *u;
+
+    for (u = acpi_table_first(); u; u = acpi_table_next(u)) {
+        struct acpi_table_header *hdr = (void *)(u - sizeof(hdr->_length));
+
+        if (memcmp(hdr->sig, "SLIC", 4) == 0) {
+            oem->id = hdr->oem_id;
+            oem->table_id = hdr->oem_table_id;
+            return 0;
+        }
+    }
+    return -1;
+}
+
 static void acpi_notify_wakeup(Notifier *notifier, void *data)
 {
     ACPIREGS *ar = container_of(notifier, ACPIREGS, wakeup);

include/hw/acpi/acpi.h

@@ -196,4 +196,11 @@ unsigned acpi_table_len(void *current);
 void acpi_table_add(const QemuOpts *opts, Error **errp);
 void acpi_table_add_builtin(const QemuOpts *opts, Error **errp);
 
+typedef struct AcpiSlicOem AcpiSlicOem;
+struct AcpiSlicOem {
+  char *id;
+  char *table_id;
+};
+int acpi_get_slic_oem(AcpiSlicOem *oem);
+
 #endif /* !QEMU_HW_ACPI_H */