[PATCH v4 4/5] staging/android: refactor SYNC_IOC_FILE_INFO

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Change SYNC_IOC_FILE_INFO behaviour to avoid future API breaks and
optimize buffer allocation. In the new approach the ioctl needs to be called
twice to retrieve the array of fence_infos pointed by info->sync_fence_info.

The first call should pass num_fences = 0, the kernel will then fill
info->num_fences. Userspace receives back the number of fences and
allocates a buffer size num_fences * sizeof(struct sync_fence_info) on
info->sync_fence_info.

It then call the ioctl again passing num_fences received in info->num_fences.
The kernel checks if info->num_fences > 0 and if yes it fill
info->sync_fence_info with an array containing all fence_infos.

info->len now represents the length of the buffer sync_fence_info points
to. Also, info->sync_fence_info was converted to __u64 pointer.

An example userspace code would be:

	struct sync_file_info *info;
	int err, size, num_fences;

	info = malloc(sizeof(*info));

	memset(info, 0, sizeof(*info));

	err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
	num_fences = info->num_fences;

	if (num_fences) {
		memset(info, 0, sizeof(*info));
		size = sizeof(struct sync_fence_info) * num_fences;
		info->len = size;
		info->num_fences = num_fences;
		info->sync_fence_info = (uint64_t) calloc(num_fences,
							  sizeof(struct sync_fence_info));

		err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
	}

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/staging/android/sync.c      | 56 +++++++++++++++++++++++++++++--------
 drivers/staging/android/uapi/sync.h |  9 +++---
 2 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index dc5f382..837cff5 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -502,21 +502,22 @@ static int sync_fill_fence_info(struct fence *fence, void *data, int size)
 static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 					unsigned long arg)
 {
-	struct sync_file_info *info;
+	struct sync_file_info in, *info;
+	struct sync_fence_info *fence_info;
 	__u32 size;
 	__u32 len = 0;
 	int ret, i;
 
-	if (copy_from_user(&size, (void __user *)arg, sizeof(size)))
+	if (copy_from_user(&in, (void __user *)arg, sizeof(*info)))
 		return -EFAULT;
 
-	if (size < sizeof(struct sync_file_info))
-		return -EINVAL;
+	if (in.status || strcmp(in.name, "\0"))
+		return -EFAULT;
 
-	if (size > 4096)
-		size = 4096;
+	if (in.num_fences && !in.sync_fence_info)
+		return -EFAULT;
 
-	info = kzalloc(size, GFP_KERNEL);
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (!info)
 		return -ENOMEM;
 
@@ -525,24 +526,55 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info->status >= 0)
 		info->status = !info->status;
 
-	info->num_fences = sync_file->num_fences;
+	/*
+	 * Passing num_fences = 0 means that userspace want to know how
+	 * many fences are in the sync_file to be able to allocate a buffer to
+	 * fit all sync_fence_infos and call the ioctl again with the buffer
+	 * assigned to info->sync_fence_info. The second call pass the
+	 * num_fences value received in the first call.
+	 */
+	if (!in.num_fences)
+		goto no_fences;
 
-	len = sizeof(struct sync_file_info);
+	size = sync_file->num_fences * sizeof(*fence_info);
+	if (in.len != size) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	fence_info = kzalloc(size, GFP_KERNEL);
+	if (!fence_info) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	for (i = 0; i < sync_file->num_fences; ++i) {
 		struct fence *fence = sync_file->cbs[i].fence;
 
-		ret = sync_fill_fence_info(fence, (u8 *)info + len, size - len);
+		ret = sync_fill_fence_info(fence, (u8 *)fence_info + len,
+					   size - len);
 
-		if (ret < 0)
+		if (ret < 0) {
+			kfree(fence_info);
 			goto out;
+		}
 
 		len += ret;
 	}
 
+	if (copy_to_user((void __user *)in.sync_fence_info, fence_info, size)) {
+		ret = -EFAULT;
+		kfree(fence_info);
+		goto out;
+	}
+
 	info->len = len;
+	info->sync_fence_info = (__u64) in.sync_fence_info;
+
+no_fences:
+	info->num_fences = sync_file->num_fences;
 
-	if (copy_to_user((void __user *)arg, info, len))
+	if (copy_to_user((void __user *)arg, info, sizeof(*info)))
 		ret = -EFAULT;
 	else
 		ret = 0;
diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
index f0b41ce..9aad623 100644
--- a/drivers/staging/android/uapi/sync.h
+++ b/drivers/staging/android/uapi/sync.h
@@ -42,21 +42,20 @@ struct sync_fence_info {
 
 /**
  * struct sync_file_info - data returned from fence info ioctl
- * @len:	ioctl caller writes the size of the buffer its passing in.
- *		ioctl returns length of sync_file_info returned to
- *		userspace including pt_info.
  * @name:	name of fence
  * @status:	status of fence. 1: signaled 0:active <0:error
  * @num_fences	number of fences in the sync_file
+ * @len:	ioctl caller writes the size of the buffer its passing in.
+ *		ioctl returns length of all fence_infos summed.
  * @sync_fence_info: array of sync_fence_info for every fence in the sync_file
  */
 struct sync_file_info {
-	__u32	len;
 	char	name[32];
 	__s32	status;
 	__u32	num_fences;
+	__u32	len;
 
-	__u8	sync_fence_info[0];
+	__u64	sync_fence_info;
 };
 
 #define SYNC_IOC_MAGIC		'>'
-- 
2.5.0