1 files changed, 100 insertions, 0 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index f90b29595927..5025563e7379 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -519,6 +519,102 @@ int simple_transaction_release(struct inode *inode, struct file *file)
         return 0;
 }
 
+/* Simple attribute files */
+
+struct simple_attr {
+        u64 (*get)(void *);
+        void (*set)(void *, u64);
+        char get_buf[24];       /* enough to store a u64 and "\n\0" */
+        char set_buf[24];
+        void *data;
+        const char *fmt;        /* format for read operation */
+        struct semaphore sem;   /* protects access to these buffers */
+};
+
+/* simple_attr_open is called by an actual attribute open file operation
+ * to set the attribute specific access operations. */
+int simple_attr_open(struct inode *inode, struct file *file,
+                     u64 (*get)(void *), void (*set)(void *, u64),
+                     const char *fmt)
+{
+        struct simple_attr *attr;
+
+        attr = kmalloc(sizeof(*attr), GFP_KERNEL);
+        if (!attr)
+                return -ENOMEM;
+
+        attr->get = get;
+        attr->set = set;
+        attr->data = inode->u.generic_ip;
+        attr->fmt = fmt;
+        init_MUTEX(&attr->sem);
+
+        file->private_data = attr;
+
+        return nonseekable_open(inode, file);
+}
+
+int simple_attr_close(struct inode *inode, struct file *file)
+{
+        kfree(file->private_data);
+        return 0;
+}
+
+/* read from the buffer that is filled with the get function */
+ssize_t simple_attr_read(struct file *file, char __user *buf,
+                         size_t len, loff_t *ppos)
+{
+        struct simple_attr *attr;
+        size_t size;
+        ssize_t ret;
+
+        attr = file->private_data;
+
+        if (!attr->get)
+                return -EACCES;
+
+        down(&attr->sem);
+        if (*ppos) /* continued read */
+                size = strlen(attr->get_buf);
+        else      /* first read */
+                size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
+                                 attr->fmt,
+                                 (unsigned long long)attr->get(attr->data));
+
+        ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
+        up(&attr->sem);
+        return ret;
+}
+
+/* interpret the buffer as a number to call the set function with */
+ssize_t simple_attr_write(struct file *file, const char __user *buf,
+                          size_t len, loff_t *ppos)
+{
+        struct simple_attr *attr;
+        u64 val;
+        size_t size;
+        ssize_t ret;
+
+        attr = file->private_data;
+
+        if (!attr->set)
+                return -EACCES;
+
+        down(&attr->sem);
+        ret = -EFAULT;
+        size = min(sizeof(attr->set_buf) - 1, len);
+        if (copy_from_user(attr->set_buf, buf, size))
+                goto out;
+
+        ret = len; /* claim we got the whole input */
+        attr->set_buf[size] = '\0';
+        val = simple_strtol(attr->set_buf, NULL, 0);
+        attr->set(attr->data, val);
+out:
+        up(&attr->sem);
+        return ret;
+}
+
 EXPORT_SYMBOL(dcache_dir_close);
 EXPORT_SYMBOL(dcache_dir_lseek);
 EXPORT_SYMBOL(dcache_dir_open);
@@ -547,3 +643,7 @@ EXPORT_SYMBOL(simple_read_from_buffer);
 EXPORT_SYMBOL(simple_transaction_get);
 EXPORT_SYMBOL(simple_transaction_read);
 EXPORT_SYMBOL(simple_transaction_release);
+EXPORT_SYMBOL_GPL(simple_attr_open);
+EXPORT_SYMBOL_GPL(simple_attr_close);
+EXPORT_SYMBOL_GPL(simple_attr_read);
+EXPORT_SYMBOL_GPL(simple_attr_write);