[dmidecode] [Patch v3] firmware: dmi-sysfs: add SMBIOS entry point area raw attribute

[Ivan Khoronzhuk]

Some utils, like dmidecode and smbios, needs to access SMBIOS entry
table area in order to get information like SMBIOS version, size, etc.
Currently it's done via /dev/mem. But for situation when /dev/mem
usage is disabled, the utils have to use dmi sysfs instead, which
doesn't represent SMBIOS entry. So this patch adds SMBIOS area to
dmi-sysfs in order to allow utils in question to work correctly with
dmi sysfs interface.

Reviewed-by: Ard Biesheuvel <address@hidden>
Signed-off-by: Ivan Khoronzhuk <address@hidden>
---

v1: https://lkml.org/lkml/2015/1/23/643
v2: https://lkml.org/lkml/2015/1/26/345

v3..v2:
  firmware: dmi_scan: add symbol to get SMBIOS entry area
  firmware: dmi-sysfs: add SMBIOS entry point area attribute
        combined in one patch
        added SMBIOS information to ABI sysfs-dmi documentaton

v2..v1:
  firmware: dmi_scan: add symbol to get SMBIOS entry area
        - used additional static var to hold SMBIOS raw table size
        - changed format of get_smbios_entry_area symbol
          returned pointer on const smbios table

  firmware: dmi-sysfs: add SMBIOS entry point area attribute
        - adopted to updated get_smbios_entry_area symbol
        - removed redundant array to save smbios table


 Documentation/ABI/testing/sysfs-firmware-dmi | 10 +++++++
 drivers/firmware/dmi-sysfs.c                 | 42 ++++++++++++++++++++++++++++
 drivers/firmware/dmi_scan.c                  | 26 +++++++++++++++++
 include/linux/dmi.h                          |  3 ++
 4 files changed, 81 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-firmware-dmi 
b/Documentation/ABI/testing/sysfs-firmware-dmi
index c78f9ab..3a9ffe8 100644
--- a/Documentation/ABI/testing/sysfs-firmware-dmi
+++ b/Documentation/ABI/testing/sysfs-firmware-dmi
@@ -12,6 +12,16 @@ Description:
                cannot ensure that the data as exported to userland is
                without error either.
 
+               The firmware provides DMI structures as a packed list of
+               data referenced by a SMBIOS table entry point. The SMBIOS
+               entry point contains general information, like SMBIOS
+               version, DMI table size, etc. The structure, content and
+               size of SMBIOS entry point is dependent on SMBIOS version.
+               That's why SMBIOS entry point is represented in dmi sysfs
+               like a raw attribute and is accessible via
+               /sys/firmware/dmi/smbios_raw_header. The format of SMBIOS
+               entry point header can be read in SMBIOS specification.
+
                DMI is structured as a large table of entries, where
                each entry has a common header indicating the type and
                length of the entry, as well as a firmware-provided
diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
index e0f1cb3..61b6a38 100644
--- a/drivers/firmware/dmi-sysfs.c
+++ b/drivers/firmware/dmi-sysfs.c
@@ -29,6 +29,8 @@
 #define MAX_ENTRY_TYPE 255 /* Most of these aren't used, but we consider
                              the top entry type is only 8 bits */
 
+static const u8 *smbios_raw_header;
+
 struct dmi_sysfs_entry {
        struct dmi_header dh;
        struct kobject kobj;
@@ -646,9 +648,37 @@ static void cleanup_entry_list(void)
        }
 }
 
+static ssize_t smbios_entry_area_raw_read(struct file *filp,
+                                         struct kobject *kobj,
+                                         struct bin_attribute *bin_attr,
+                                         char *buf, loff_t pos, size_t count)
+{
+       ssize_t size;
+
+       size = bin_attr->size;
+
+       if (size > pos)
+               size -= pos;
+       else
+               return 0;
+
+       if (count < size)
+               size = count;
+
+       memcpy(buf, &smbios_raw_header[pos], size);
+
+       return size;
+}
+
+static struct bin_attribute smbios_raw_area_attr = {
+       .read = smbios_entry_area_raw_read,
+       .attr = {.name = "smbios_raw_header", .mode = 0400},
+};
+
 static int __init dmi_sysfs_init(void)
 {
        int error = -ENOMEM;
+       int size;
        int val;
 
        /* Set up our directory */
@@ -669,6 +699,18 @@ static int __init dmi_sysfs_init(void)
                goto err;
        }
 
+       smbios_raw_header = dmi_get_smbios_entry_area(&size);
+       if (!smbios_raw_header) {
+               pr_debug("dmi-sysfs: SMBIOS raw data is not available.\n");
+               error = -ENODATA;
+               goto err;
+       }
+
+       /* Create the raw binary file to access the entry area */
+       smbios_raw_area_attr.size = size;
+       if (sysfs_create_bin_file(dmi_kobj, &smbios_raw_area_attr))
+               goto err;
+
        pr_debug("dmi-sysfs: loaded.\n");
 
        return 0;
diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 420c8d8..d94c6b7 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -113,6 +113,8 @@ static void dmi_table(u8 *buf, int len, int num,
        }
 }
 
+static unsigned char smbios_header[32];
+static int smbios_header_size;
 static phys_addr_t dmi_base;
 static u16 dmi_len;
 static u16 dmi_num;
@@ -474,6 +476,8 @@ static int __init dmi_present(const u8 *buf)
        if (memcmp(buf, "_SM_", 4) == 0 &&
            buf[5] < 32 && dmi_checksum(buf, buf[5])) {
                smbios_ver = get_unaligned_be16(buf + 6);
+               smbios_header_size = buf[5];
+               memcpy(smbios_header, buf, smbios_header_size);
 
                /* Some BIOS report weird SMBIOS version, fix that up */
                switch (smbios_ver) {
@@ -505,6 +509,8 @@ static int __init dmi_present(const u8 *buf)
                                pr_info("SMBIOS %d.%d present.\n",
                                       dmi_ver >> 8, dmi_ver & 0xFF);
                        } else {
+                               smbios_header_size = 15;
+                               memcpy(smbios_header, buf, smbios_header_size);
                                dmi_ver = (buf[14] & 0xF0) << 4 |
                                           (buf[14] & 0x0F);
                                pr_info("Legacy DMI %d.%d present.\n",
@@ -531,6 +537,8 @@ static int __init dmi_smbios3_present(const u8 *buf)
                dmi_ver &= 0xFFFFFF;
                dmi_len = get_unaligned_le32(buf + 12);
                dmi_base = get_unaligned_le64(buf + 16);
+               smbios_header_size = buf[6];
+               memcpy(smbios_header, buf, smbios_header_size);
 
                /*
                 * The 64-bit SMBIOS 3.0 entry point no longer has a field
@@ -944,3 +952,21 @@ void dmi_memdev_name(u16 handle, const char **bank, const 
char **device)
        }
 }
 EXPORT_SYMBOL_GPL(dmi_memdev_name);
+
+/**
+ * dmi_get_smbios_entry_area - copy SMBIOS entry point area to array.
+ * @size - pointer to assign actual size of SMBIOS entry point area.
+ *
+ * returns NULL if table is not available, otherwise returns pointer on
+ * SMBIOS entry point area array.
+ */
+const u8 *dmi_get_smbios_entry_area(int *size)
+{
+       if (!smbios_header_size || !dmi_available)
+               return NULL;
+
+       *size = smbios_header_size;
+
+       return smbios_header;
+}
+EXPORT_SYMBOL_GPL(dmi_get_smbios_entry_area);
diff --git a/include/linux/dmi.h b/include/linux/dmi.h
index f820f0a..8e1a28d 100644
--- a/include/linux/dmi.h
+++ b/include/linux/dmi.h
@@ -109,6 +109,7 @@ extern int dmi_walk(void (*decode)(const struct dmi_header 
*, void *),
        void *private_data);
 extern bool dmi_match(enum dmi_field f, const char *str);
 extern void dmi_memdev_name(u16 handle, const char **bank, const char 
**device);
+const u8 *dmi_get_smbios_entry_area(int *size);
 
 #else
 
@@ -140,6 +141,8 @@ static inline void dmi_memdev_name(u16 handle, const char 
**bank,
                const char **device) { }
 static inline const struct dmi_system_id *
        dmi_first_match(const struct dmi_system_id *list) { return NULL; }
+static inline const u8 *dmi_get_smbios_entry_area(int *size)
+       { return NULL; }
 
 #endif
 
-- 
1.9.1