[BK PATCH] add SMBIOS tables to sysfs

Michael Brown
2004-04-28T02:30:04Z

Andrew,
Below is a short patch to add SMBIOS data to sysfs. It it against latest
bitkeeper 2.6.6-rc (specifically, it applies after the efivars patch that
recently went in) but should apply to any recent kernel with only minor
reject on drivers/firmware/Makefile. A version for 2.4 (using /proc) will
follow tomorrow.

--Rationale--

In the past, systems management applications that wanted to parse the
SMBIOS tables used the /dev/mem interface to directly read the table
header + data from physical memory. The spec says that the table header
(sometimes referred to as the table entry point) should be somewhere in memory
between 0xF0000 and 0xFFFFF. The table header contains a 32-bit pointer to the
table proper. Up until this point, most BIOS implementations put the actual
table in F-block as well.

This is changing. Many systems want to do dynamic SMBIOS tables, and some
systems are running out of memory in F-block to store the table. On these
systems, the actual SMBIOS table is typically in high memory somewhere in an
E820 reserved section. The normal /dev/mem driver will not allow access to
these regions.

Next, in Red Hat 2.6 kernels, the /dev/mem interface has been restricted
so that it will only allow access to the first 1MB of RAM for security purposes.

And last, access to /dev/mem is allowed only to users with CAP_SYS_RAWIO.

So, to get around these restrictions here is a small SMBIOS driver that
presents existing SMBIOS information as files in sysfs. It creates
/sys/firmware/smbios/smbios/table_entry_point, and
/sys/firmware/smbios/smbios/table. These files are binary-mode files that
contain the raw contents of the table entry point and table, respectively.
These files can easily be parsed by userspace apps.

--
Michael Brown

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
# 2004/04/27 20:27:21-05:00 mebrown@michaels-house.net
# Add sysfs driver to present SMBIOS data
#
# drivers/firmware/smbios.h
# 2004/04/27 20:25:16-05:00 mebrown@michaels-house.net +53 -0
#
# drivers/firmware/smbios.h
# 2004/04/27 20:25:16-05:00 mebrown@michaels-house.net +0 -0
# BitKeeper file /home/michael_e_brown/kernel/bk/subtrees/smbios-driver-work2/drivers/firmware/smbios.h
#
# drivers/firmware/smbios.c
# 2004/04/27 20:25:15-05:00 mebrown@michaels-house.net +266 -0
#
# drivers/firmware/smbios.c
# 2004/04/27 20:25:15-05:00 mebrown@michaels-house.net +0 -0
# BitKeeper file /home/michael_e_brown/kernel/bk/subtrees/smbios-driver-work2/drivers/firmware/smbios.c
#
# drivers/firmware/Makefile
# 2004/04/27 20:25:15-05:00 mebrown@michaels-house.net +1 -0
# add SMBIOS to build system
#
# drivers/firmware/Kconfig
# 2004/04/27 20:25:15-05:00 mebrown@michaels-house.net +8 -0
# Add SMBIOS sysfs config option
#
diff -Nru a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
--- a/drivers/firmware/Kconfig Tue Apr 27 20:28:39 2004
+++ b/drivers/firmware/Kconfig Tue Apr 27 20:28:39 2004
@@ -34,4 +34,12 @@
Subsequent efibootmgr releases may be found at:
http://linux.dell.com/efibootmgr

+config SMBIOS
+ tristate "BIOS SMBIOS table access driver."
+ help
+ Say Y or M here if you want to enable access to the SMBIOS table
+ via driverfs. It exposes /sys/firmware/smbios/ subdirectory tree
+ containing a binary dump of the SMBIOS table header as well as the SMBIOS
+ table.
+
endmenu
diff -Nru a/drivers/firmware/Makefile b/drivers/firmware/Makefile
--- a/drivers/firmware/Makefile Tue Apr 27 20:28:39 2004
+++ b/drivers/firmware/Makefile Tue Apr 27 20:28:39 2004
@@ -3,3 +3,4 @@
#
obj-$(CONFIG_EDD) += edd.o
obj-$(CONFIG_EFI_VARS) += efivars.o
+obj-$(CONFIG_SMBIOS) += smbios.o
diff -Nru a/drivers/firmware/smbios.c b/drivers/firmware/smbios.c
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/drivers/firmware/smbios.c Tue Apr 27 20:28:39 2004
@@ -0,0 +1,266 @@
+/*
+ * linux/drivers/firmware/smbios.c
+ * Copyright (C) 2002, 2003, 2004 Dell Inc.
+ * by Michael Brown <Michael_E_Brown@dell.com>
+ * vim:noet:ts=8:sw=8:filetype=c:textwidth=80:
+ *
+ * BIOS SMBIOS Table access
+ * conformant to DMTF SMBIOS definition
+ * at http://www.dmtf.org/standards/smbios
+ *
+ * This code takes information provided by SMBIOS tables
+ * and presents it in sysfs as:
+ * /sys/firmware/smbios/smbios
+ * |--> /table_entry_point
+ * |--> /table
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License v2.0 as published by
+ * the Free Software Foundation
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <asm/io.h>
+#include <asm/uaccess.h>
+#include "smbios.h"
+
+MODULE_AUTHOR("Michael Brown <Michael_E_Brown@Dell.com>");
+MODULE_DESCRIPTION("sysfs interface to SMBIOS information");
+MODULE_LICENSE("GPL");
+
+#define SMBIOS_VERSION "1.0 2004-04-19"
+
+struct smbios_device {
+ struct smbios_table_entry_point table_eps;
+ unsigned int smbios_table_real_length;
+ struct kobject kobj;
+};
+
+/* there shall be only one */
+static struct smbios_device the_smbios_device;
+
+#define to_smbios_device(obj) container_of(obj,struct smbios_device,kobj)
+
+/* don't currently have any "normal" attributes, so we don't need a way to
+ * show them. */
+static struct sysfs_ops smbios_attr_ops = { };
+
+static __init int
+checksum_eps(struct smbios_table_entry_point *table_eps)
+{
+ u8 *p = (u8 *)table_eps;
+ u8 checksum = 0;
+ int i=0;
+ for (i=0; i < table_eps->eps_length && i < sizeof(*table_eps); ++i) {
+ checksum += p[i];
+ }
+ return( checksum == 0 );
+}
+
+static __init int
+find_table_entry_point(struct smbios_device *sdev)
+{
+ struct smbios_table_entry_point *table_eps = &(sdev->table_eps);
+ u32 fp = 0xF0000;
+ while (fp < 0xFFFFF) {
+ isa_memcpy_fromio(table_eps, fp, sizeof(*table_eps));
+ if (memcmp(table_eps->anchor, "_SM_", 4)==0 &&
+ checksum_eps(table_eps)) {
+ return 0;
+ }
+ fp += 16;
+ }
+
+ printk(KERN_INFO "SMBIOS table entry point not found in "
+ "0xF0000 - 0xFFFFF\n");
+ return -ENODEV;
+}
+
+static __init int
+find_table_max_address(struct smbios_device *sdev)
+{
+ /* break out on one of three conditions:
+ * -- hit table_eps.table_length
+ * -- hit number of items that table claims we have
+ * -- hit structure type 127
+ */
+
+ u8 *buf = ioremap(sdev->table_eps.table_address,
+ sdev->table_eps.table_length);
+ u8 *ptr = buf;
+ int count = 0, keep_going = 1;
+ int max_count = sdev->table_eps.table_num_structs;
+ int max_length = sdev->table_eps.table_length;
+ while(keep_going && ((ptr - buf) <= max_length) && count < max_count){
+ if( ptr[0] == 0x7F ) /* ptr[0] is type */
+ keep_going = 0;
+
+ ptr += ptr[1]; /* ptr[1] is length, skip structure */
+ /* skip strings at end of structure */
+ while((ptr-buf) < max_length && (ptr[0] || ptr[1]))
+ ++ptr;
+
+ /* string area ends in double-null. skip it. */
+ ptr += 2;
+ ++count;
+ }
+ sdev->smbios_table_real_length = (ptr - buf);
+ iounmap(buf);
+
+ if( count != max_count )
+ printk(KERN_INFO "Warning: SMBIOS table structure count"
+ " does not match count specified in the"
+ " table entry point.\n"
+ " Table entry point count: %d\n"
+ " Actual count: %d\n",
+ max_count, count );
+
+ if(keep_going != 0)
+ printk(KERN_INFO "Warning: SMBIOS table does not end with a"
+ " structure type 127. This may indicate a"
+ " truncated table.");
+
+ if(sdev->smbios_table_real_length != max_length)
+ printk(KERN_INFO "Warning: BIOS specified SMBIOS table length"
+ " does not match calculated length.\n"
+ " BIOS specified: %d\n"
+ " calculated length: %d\n",
+ max_length, sdev->smbios_table_real_length);
+
+ return sdev->smbios_table_real_length;
+}
+
+static ssize_t
+smbios_read_table_entry_point(struct kobject *kobj, char *buffer,
+ loff_t pos, size_t size)
+{
+ struct smbios_device *sdev = to_smbios_device(kobj);
+ const char *p = (const char *)&(sdev->table_eps);
+ unsigned int count =
+ size > sizeof(sdev->table_eps) ?
+ sizeof(sdev->table_eps) : size;
+ memcpy( buffer, p, count );
+ return count;
+}
+
+static ssize_t
+smbios_read_table(struct kobject *kobj, char *buffer,
+ loff_t pos, size_t size)
+{
+ struct smbios_device *sdev = to_smbios_device(kobj);
+ u8 *buf;
+ unsigned int count = sdev->smbios_table_real_length - pos;
+ int i = 0;
+ count = count < size ? count : size;
+
+ if (pos > sdev->smbios_table_real_length)
+ return 0;
+
+ buf = ioremap(sdev->table_eps.table_address, sdev->smbios_table_real_length);
+ if (buf == NULL)
+ return -ENXIO;
+
+ /* memcpy( buffer, buf+pos, count ); */
+ for (i = 0; i < count; ++i) {
+ buffer[i] = readb( buf+pos+i );
+ }
+
+ iounmap(buf);
+
+ return count;
+}
+
+static struct bin_attribute tep_attr = {
+ .attr = {.name = "table_entry_point", .owner = THIS_MODULE, .mode = 0444},
+ .size = sizeof(struct smbios_table_entry_point),
+ .read = smbios_read_table_entry_point,
+ /* not writeable */
+};
+
+static struct bin_attribute table_attr = {
+ .attr = { .name = "table", .owner = THIS_MODULE, .mode = 0444 },
+ /* size set later, we don't know it here. */
+ .read = smbios_read_table,
+ /* not writeable */
+};
+
+/* no default attributes yet. */
+static struct attribute * def_attrs[] = { NULL, };
+
+static struct kobj_type ktype_smbios = {
+ .sysfs_ops = &smbios_attr_ops,
+ .default_attrs = def_attrs,
+ /* statically allocated, no release method necessary */
+};
+
+static decl_subsys(smbios,&ktype_smbios,NULL);
+
+static inline void
+smbios_device_unregister(struct smbios_device *sdev)
+{
+ sysfs_remove_bin_file(&sdev->kobj, &tep_attr );
+ sysfs_remove_bin_file(&sdev->kobj, &table_attr );
+ kobject_unregister(&sdev->kobj);
+}
+
+static int
+smbios_device_register(struct smbios_device *sdev)
+{
+ int error;
+
+ if (!sdev)
+ return 1;
+
+ snprintf(sdev->kobj.name, 7, "smbios" );
+ kobj_set_kset_s(sdev,smbios_subsys);
+ error = kobject_register(&sdev->kobj);
+ if (!error){
+ sysfs_create_bin_file(&sdev->kobj, &tep_attr );
+ sysfs_create_bin_file(&sdev->kobj, &table_attr );
+ }
+ return error;
+}
+
+static int __init
+smbios_init(void)
+{
+ int rc=0;
+
+ printk(KERN_INFO "SMBIOS facility v%s\n", SMBIOS_VERSION );
+
+ rc = find_table_entry_point(&the_smbios_device);
+ if (rc)
+ return rc;
+
+ table_attr.size = find_table_max_address(&the_smbios_device);
+
+ rc = firmware_register(&smbios_subsys);
+ if (rc)
+ return rc;
+
+ rc = smbios_device_register(&the_smbios_device);
+
+ if (rc)
+ firmware_unregister(&smbios_subsys);
+
+ return rc;
+}
+
+static void __exit
+smbios_exit(void)
+{
+ smbios_device_unregister(&the_smbios_device);
+ firmware_unregister(&smbios_subsys);
+}
+
+late_initcall(smbios_init);
+module_exit(smbios_exit);
diff -Nru a/drivers/firmware/smbios.h b/drivers/firmware/smbios.h
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/drivers/firmware/smbios.h Tue Apr 27 20:28:39 2004
@@ -0,0 +1,53 @@
+/*
+ * linux/drivers/firmware/smbios.c
+ * Copyright (C) 2002, 2003, 2004 Dell Inc.
+ * by Michael Brown <Michael_E_Brown@dell.com>
+ * vim:noet:ts=8:sw=8:filetype=c:textwidth=80:
+ *
+ * BIOS SMBIOS Table access
+ * conformant to DMTF SMBIOS definition
+ * at http://www.dmtf.org/standards/smbios
+ *
+ * This code takes information provided by SMBIOS tables
+ * and presents it in sysfs.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License v2.0 as published by
+ * the Free Software Foundation
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#ifndef _LINUX_SMBIOS_H
+#define _LINUX_SMBIOS_H
+
+#include <linux/types.h>
+
+struct smbios_table_entry_point {
+ u8 anchor[4];
+ u8 checksum;
+ u8 eps_length;
+ u8 major_ver;
+ u8 minor_ver;
+ u16 max_struct_size;
+ u8 revision;
+ u8 formatted_area[5];
+ u8 dmi_anchor[5];
+ u8 intermediate_checksum;
+ u16 table_length;
+ u32 table_address;
+ u16 table_num_structs;
+ u8 smbios_bcd_revision;
+} __attribute__ ((packed));
+
+struct smbios_structure_header {
+ u8 type;
+ u8 length;
+ u16 handle;
+} __attribute__ ((packed));
+
+#endif /* _LINUX_SMBIOS_H */