[PATCH] powerpc/powernv/prd: Allow copying partial data to user space

[Vasant Hegde]

Allow copying partial data to user space. So that opal-prd daemon
can read message size, reallocate memory and make read call to
get rest of the data.

Cc: Jeremy Kerr <j...@ozlabs.org>
Cc: Vaidyanathan Srinivasan <sva...@linux.vnet.ibm.com>
Signed-off-by: Vasant Hegde <hegdevas...@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/powernv/opal-prd.c | 27 ++++++++---------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/opal-prd.c 
b/arch/powerpc/platforms/powernv/opal-prd.c
index 45f4223a790f..dac9d18293d8 100644
--- a/arch/powerpc/platforms/powernv/opal-prd.c
+++ b/arch/powerpc/platforms/powernv/opal-prd.c
@@ -153,20 +153,15 @@ static __poll_t opal_prd_poll(struct file *file,
 static ssize_t opal_prd_read(struct file *file, char __user *buf,
                size_t count, loff_t *ppos)
 {
-       struct opal_prd_msg_queue_item *item;
+       struct opal_prd_msg_queue_item *item = NULL;
        unsigned long flags;
-       ssize_t size, err;
+       ssize_t size;
        int rc;
 
        /* we need at least a header's worth of data */
        if (count < sizeof(item->msg))
                return -EINVAL;
 
-       if (*ppos)
-               return -ESPIPE;
-
-       item = NULL;
-
        for (;;) {
 
                spin_lock_irqsave(&opal_prd_msg_queue_lock, flags);
@@ -190,27 +185,23 @@ static ssize_t opal_prd_read(struct file *file, char 
__user *buf,
        }
 
        size = be16_to_cpu(item->msg.size);
-       if (size > count) {
-               err = -EINVAL;
+       rc = simple_read_from_buffer(buf, count, ppos, &item->msg, size);
+       if (rc < 0)
                goto err_requeue;
-       }
-
-       rc = copy_to_user(buf, &item->msg, size);
-       if (rc) {
-               err = -EFAULT;
+       if (*ppos < size)
                goto err_requeue;
-       }
 
+       /* Reset position */
+       *ppos = 0;
        kfree(item);
-
-       return size;
+       return rc;
 
 err_requeue:
        /* eep! re-queue at the head of the list */
        spin_lock_irqsave(&opal_prd_msg_queue_lock, flags);
        list_add(&item->list, &opal_prd_msg_queue);
        spin_unlock_irqrestore(&opal_prd_msg_queue_lock, flags);
-       return err;
+       return rc;
 }
 
 static ssize_t opal_prd_write(struct file *file, const char __user *buf,
-- 
2.21.0