sparc: Add support for seek and shorter read to /dev/mdesc

/dev/mdesc on Linux does not support reading arbitrary number
of bytes and seeking while /dev/mdesc on Solaris does. This
causes tools that work on Solaris to break on Linux. This patch
adds these two capabilities to /dev/mdesc.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 69 insertions, 13 deletions

diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index a1a4400d4025..99632a87e697 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -906,29 +906,85 @@ void mdesc_fill_in_cpu_data(cpumask_t *mask)
         smp_fill_in_sib_core_maps();
 }
 
-static ssize_t mdesc_read(struct file *file, char __user *buf,
-                          size_t len, loff_t *offp)
+/* mdesc_open() - Grab a reference to mdesc_handle when /dev/mdesc is
+ * opened. Hold this reference until /dev/mdesc is closed to ensure
+ * mdesc data structure is not released underneath us. Store the
+ * pointer to mdesc structure in private_data for read and seek to use
+ */
+static int mdesc_open(struct inode *inode, struct file *file)
 {
         struct mdesc_handle *hp = mdesc_grab();
-        int err;
 
         if (!hp)
                 return -ENODEV;
 
-        err = hp->handle_size;
-        if (len < hp->handle_size)
-                err = -EMSGSIZE;
-        else if (copy_to_user(buf, &hp->mdesc, hp->handle_size))
-                err = -EFAULT;
-        mdesc_release(hp);
+        file->private_data = hp;
+
+        return 0;
+}
+
+static ssize_t mdesc_read(struct file *file, char __user *buf,
+                          size_t len, loff_t *offp)
+{
+        struct mdesc_handle *hp = file->private_data;
+        unsigned char *mdesc;
+        int bytes_left, count = len;
+
+        if (*offp >= hp->handle_size)
+                return 0;
+
+        bytes_left = hp->handle_size - *offp;
+        if (count > bytes_left)
+                count = bytes_left;
+
+        mdesc = (unsigned char *)&hp->mdesc;
+        mdesc += *offp;
+        if (!copy_to_user(buf, mdesc, count)) {
+                *offp += count;
+                return count;
+        } else {
+                return -EFAULT;
+        }
+}
 
-        return err;
+static loff_t mdesc_llseek(struct file *file, loff_t offset, int whence)
+{
+        struct mdesc_handle *hp;
+
+        switch (whence) {
+        case SEEK_CUR:
+                offset += file->f_pos;
+                break;
+        case SEEK_SET:
+                break;
+        default:
+                return -EINVAL;
+        }
+
+        hp = file->private_data;
+        if (offset > hp->handle_size)
+                return -EINVAL;
+        else
+                file->f_pos = offset;
+
+        return offset;
+}
+
+/* mdesc_close() - /dev/mdesc is being closed, release the reference to
+ * mdesc structure.
+ */
+static int mdesc_close(struct inode *inode, struct file *file)
+{
+        mdesc_release(file->private_data);
+        return 0;
 }
 
 static const struct file_operations mdesc_fops = {
-        .read   = mdesc_read,
-        .owner  = THIS_MODULE,
-        .llseek = noop_llseek,
+        .open    = mdesc_open,
+        .read    = mdesc_read,
+        .llseek  = mdesc_llseek,
+        .release = mdesc_close,
+        .owner   = THIS_MODULE,
 };
 
 static struct miscdevice mdesc_misc = {