firewire: add fw_csr_string() helper function

The core (sysfs attributes), the firedtv driver, and possible future
drivers all read strings from some configuration ROM directory.  Factor
out the generic code from show_text_leaf() into a new helper function,
modified slightly to handle arbitrary buffer sizes.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

2 files changed, 82 insertions, 67 deletions

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index 9d0dfcbe2c1c..a39e4344cd58 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -59,6 +59,67 @@ int fw_csr_iterator_next(struct fw_csr_iterator *ci, int *key, int *value)
 }
 EXPORT_SYMBOL(fw_csr_iterator_next);
 
+static u32 *search_leaf(u32 *directory, int search_key)
+{
+        struct fw_csr_iterator ci;
+        int last_key = 0, key, value;
+
+        fw_csr_iterator_init(&ci, directory);
+        while (fw_csr_iterator_next(&ci, &key, &value)) {
+                if (last_key == search_key &&
+                    key == (CSR_DESCRIPTOR | CSR_LEAF))
+                        return ci.p - 1 + value;
+                last_key = key;
+        }
+        return NULL;
+}
+
+static int textual_leaf_to_string(u32 *block, char *buf, size_t size)
+{
+        unsigned int quadlets, length;
+
+        if (!size || !buf)
+                return -EINVAL;
+
+        quadlets = min(block[0] >> 16, 256u);
+        if (quadlets < 2)
+                return -ENODATA;
+
+        if (block[1] != 0 || block[2] != 0)
+                /* unknown language/character set */
+                return -ENODATA;
+
+        block += 3;
+        quadlets -= 2;
+        for (length = 0; length < quadlets * 4 && length + 1 < size; length++) {
+                char c = block[length / 4] >> (24 - 8 * (length % 4));
+                if (c == '\0')
+                        break;
+                buf[length] = c;
+        }
+        buf[length] = '\0';
+        return length;
+}
+
+/**
+ * fw_csr_string - reads a string from the configuration ROM
+ * @directory: device or unit directory;
+ *             fw_device->config_rom+5 or fw_unit->directory
+ * @key: the key of the preceding directory entry
+ * @buf: where to put the string
+ * @size: size of @buf, in bytes
+ *
+ * Returns string length (>= 0) or error code (< 0).
+ */
+int fw_csr_string(u32 *directory, int key, char *buf, size_t size)
+{
+        u32 *leaf = search_leaf(directory, key);
+        if (!leaf)
+                return -ENOENT;
+        return textual_leaf_to_string(leaf, buf, size);
+}
+EXPORT_SYMBOL(fw_csr_string);
+
 static bool is_fw_unit(struct device *dev);
 
 static int match_unit_directory(u32 *directory, u32 match_flags,
@@ -226,10 +287,10 @@ static ssize_t show_text_leaf(struct device *dev,
 {
         struct config_rom_attribute *attr =
                 container_of(dattr, struct config_rom_attribute, attr);
-        struct fw_csr_iterator ci;
-        u32 *dir, *block = NULL, *p, *end;
-        int length, key, value, last_key = 0, ret = -ENOENT;
-        char *b;
+        u32 *dir;
+        size_t bufsize;
+        char dummy_buf[2];
+        int ret;
 
         down_read(&fw_device_rwsem);
 
@@ -238,40 +299,23 @@ static ssize_t show_text_leaf(struct device *dev,
         else
                 dir = fw_device(dev)->config_rom + 5;
 
-        fw_csr_iterator_init(&ci, dir);
-        while (fw_csr_iterator_next(&ci, &key, &value)) {
-                if (attr->key == last_key &&
-                    key == (CSR_DESCRIPTOR | CSR_LEAF))
-                        block = ci.p - 1 + value;
-                last_key = key;
+        if (buf) {
+                bufsize = PAGE_SIZE - 1;
+        } else {
+                buf = dummy_buf;
+                bufsize = 1;
         }
 
-        if (block == NULL)
-                goto out;
-
-        length = min(block[0] >> 16, 256U);
-        if (length < 3)
-                goto out;
-
-        if (block[1] != 0 || block[2] != 0)
-                /* Unknown encoding. */
-                goto out;
+        ret = fw_csr_string(dir, attr->key, buf, bufsize);
 
-        if (buf == NULL) {
-                ret = length * 4;
-                goto out;
+        if (ret >= 0) {
+                /* Strip trailing whitespace and add newline. */
+                while (ret > 0 && isspace(buf[ret - 1]))
+                        ret--;
+                strcpy(buf + ret, "\n");
+                ret++;
         }
 
-        b = buf;
-        end = &block[length + 1];
-        for (p = &block[3]; p < end; p++, b += 4)
-                * (u32 *) b = (__force u32) __cpu_to_be32(*p);
-
-        /* Strip trailing whitespace and add newline. */
-        while (b--, (isspace(*b) || *b == '\0') && b > buf);
-        strcpy(b + 1, "\n");
-        ret = b + 2 - buf;
- out:
         up_read(&fw_device_rwsem);
 
         return ret;
diff --git a/drivers/media/dvb/firewire/firedtv-fw.c b/drivers/media/dvb/firewire/firedtv-fw.c
index 6223bf01efe9..4253b7ab0097 100644
--- a/drivers/media/dvb/firewire/firedtv-fw.c
+++ b/drivers/media/dvb/firewire/firedtv-fw.c
@@ -239,47 +239,18 @@ static const struct fw_address_region fcp_region = {
 };
 
 /* Adjust the template string if models with longer names appear. */
-#define MAX_MODEL_NAME_LEN ((int)DIV_ROUND_UP(sizeof("FireDTV ????"), 4))
-
-static size_t model_name(u32 *directory, __be32 *buffer)
-{
-        struct fw_csr_iterator ci;
-        int i, length, key, value, last_key = 0;
-        u32 *block = NULL;
-
-        fw_csr_iterator_init(&ci, directory);
-        while (fw_csr_iterator_next(&ci, &key, &value)) {
-                if (last_key == CSR_MODEL &&
-                    key == (CSR_DESCRIPTOR | CSR_LEAF))
-                        block = ci.p - 1 + value;
-                last_key = key;
-        }
-
-        if (block == NULL)
-                return 0;
-
-        length = min((int)(block[0] >> 16) - 2, MAX_MODEL_NAME_LEN);
-        if (length <= 0)
-                return 0;
-
-        /* fast-forward to text string */
-        block += 3;
-
-        for (i = 0; i < length; i++)
-                buffer[i] = cpu_to_be32(block[i]);
-
-        return length * 4;
-}
+#define MAX_MODEL_NAME_LEN sizeof("FireDTV ????")
 
 static int node_probe(struct device *dev)
 {
         struct firedtv *fdtv;
-        __be32 name[MAX_MODEL_NAME_LEN];
+        char name[MAX_MODEL_NAME_LEN];
         int name_len, err;
 
-        name_len = model_name(fw_unit(dev)->directory, name);
+        name_len = fw_csr_string(fw_unit(dev)->directory, CSR_MODEL,
+                                 name, sizeof(name));
 
-        fdtv = fdtv_alloc(dev, &backend, (char *)name, name_len);
+        fdtv = fdtv_alloc(dev, &backend, name, name_len >= 0 ? name_len : 0);
         if (!fdtv)
                 return -ENOMEM;