[PATCH v12 2/2] staging/android: refactor SYNC IOCTLs

[Gustavo Padovan]

From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>

Change SYNC_IOC_FILE_INFO (former SYNC_IOC_FENCE_INFO) behaviour to avoid
future API breaks and optimize buffer allocation.

Now num_fences can be filled by the caller to inform how many fences it
wants to retrieve from the kernel. If the num_fences passed is greater
than zero info->sync_fence_info should point to a buffer with enough space
to fit all fences.

However if num_fences passed to the kernel is 0, the kernel will reply
with number of fences of the sync_file.

Sending first an ioctl with num_fences = 0 can optimize buffer allocation,
in a first call with num_fences = 0 userspace will receive the actual
number of fences in the num_fences filed.

Then it can allocate a buffer with the correct size on sync_fence_info and
call SYNC_IOC_FILE_INFO again, but now with the actual value of num_fences
in the sync_file.

info->sync_fence_info was converted to __u64 pointer to prevent 32bit
compatibility issues. And a flags member was added.

An example userspace code for the later would be:

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

	info = malloc(sizeof(*info));

	info.flags = 0;
	err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
	num_fences = info->num_fences;

	if (num_fences) {
		info.flags = 0;
		size = sizeof(struct sync_fence_info) * num_fences;
		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);
	}

Finally the IOCTLs numbers were changed to avoid any potential old
userspace running the old API to get weird errors. Changing the opcodes
will make them fail right away. This is just a precaution, there no
upstream users of these interfaces yet and the only user is Android, but
we don't expect anyone trying to run android userspace and all it
dependencies on top of upstream kernels.

Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Acked-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Acked-by: Rob Clark <robdclark@xxxxxxxxx>
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

---
v2: fix fence_info memory leak

v3: Comments from Emil Velikov
	- improve commit message
	- remove __u64 cast
	- remove check for output fields in file_info
	- clean up sync_fill_fence_info()

    Comments from Maarten Lankhorst
	- remove in.num_fences && !in.sync_fence_info check
	- remove info->len and use only num_fences to calculate size

    Comments from Dan Carpenter
	- fix info->sync_fence_info documentation

v4: remove allocated struct sync_file_info (comment from Maarten)

v5: merge all commits that were changing the ABI

v6: fix -Wint-to-pointer-cast error on info.sync_fence_info
---
 drivers/staging/android/sync.c      | 76 ++++++++++++++++++++-----------------
 drivers/staging/android/uapi/sync.h | 36 +++++++++++++-----
 2 files changed, 67 insertions(+), 45 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index 3a8f210..f9c6094 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -445,6 +445,11 @@ static long sync_file_ioctl_merge(struct sync_file *sync_file,
 		goto err_put_fd;
 	}
 
+	if (data.flags || data.pad) {
+		err = -EINVAL;
+		goto err_put_fd;
+	}
+
 	fence2 = sync_file_fdget(data.fd2);
 	if (!fence2) {
 		err = -ENOENT;
@@ -479,13 +484,9 @@ err_put_fd:
 	return err;
 }
 
-static int sync_fill_fence_info(struct fence *fence, void *data, int size)
+static void sync_fill_fence_info(struct fence *fence,
+				struct sync_fence_info *info)
 {
-	struct sync_fence_info *info = data;
-
-	if (size < sizeof(*info))
-		return -ENOMEM;
-
 	strlcpy(info->obj_name, fence->ops->get_timeline_name(fence),
 		sizeof(info->obj_name));
 	strlcpy(info->driver_name, fence->ops->get_driver_name(fence),
@@ -495,58 +496,63 @@ static int sync_fill_fence_info(struct fence *fence, void *data, int size)
 	else
 		info->status = 0;
 	info->timestamp_ns = ktime_to_ns(fence->timestamp);
-
-	return sizeof(*info);
 }
 
 static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 					unsigned long arg)
 {
-	struct sync_file_info *info;
+	struct sync_file_info info;
+	struct sync_fence_info *fence_info = NULL;
 	__u32 size;
-	__u32 len = 0;
 	int ret, i;
 
-	if (copy_from_user(&size, (void __user *)arg, sizeof(size)))
+	if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
 		return -EFAULT;
 
-	if (size < sizeof(struct sync_file_info))
+	if (info.flags || info.pad)
 		return -EINVAL;
 
-	if (size > 4096)
-		size = 4096;
-
-	info = kzalloc(size, GFP_KERNEL);
-	if (!info)
-		return -ENOMEM;
-
-	strlcpy(info->name, sync_file->name, sizeof(info->name));
-	info->status = atomic_read(&sync_file->status);
-	if (info->status >= 0)
-		info->status = !info->status;
-
-	len = sizeof(struct sync_file_info);
+	/*
+	 * Passing num_fences = 0 means that userspace doesn't want to
+	 * retrieve any sync_fence_info. If num_fences = 0 we skip filling
+	 * sync_fence_info and return the actual number of fences on
+	 * info->num_fences.
+	 */
+	if (!info.num_fences)
+		goto no_fences;
 
-	for (i = 0; i < sync_file->num_fences; ++i) {
-		struct fence *fence = sync_file->cbs[i].fence;
+	if (info.num_fences < sync_file->num_fences)
+		return -EINVAL;
 
-		ret = sync_fill_fence_info(fence, (u8 *)info + len, size - len);
+	size = sync_file->num_fences * sizeof(*fence_info);
+	fence_info = kzalloc(size, GFP_KERNEL);
+	if (!fence_info)
+		return -ENOMEM;
 
-		if (ret < 0)
-			goto out;
+	for (i = 0; i < sync_file->num_fences; ++i)
+		sync_fill_fence_info(sync_file->cbs[i].fence, &fence_info[i]);
 
-		len += ret;
+	if (copy_to_user(u64_to_user_ptr(info.sync_fence_info), fence_info,
+			 size)) {
+		ret = -EFAULT;
+		goto out;
 	}
 
-	info->len = len;
+no_fences:
+	strlcpy(info.name, sync_file->name, sizeof(info.name));
+	info.status = atomic_read(&sync_file->status);
+	if (info.status >= 0)
+		info.status = !info.status;
+
+	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;
 
 out:
-	kfree(info);
+	kfree(fence_info);
 
 	return ret;
 }
@@ -560,7 +566,7 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd,
 	case SYNC_IOC_MERGE:
 		return sync_file_ioctl_merge(sync_file, arg);
 
-	case SYNC_IOC_FENCE_INFO:
+	case SYNC_IOC_FILE_INFO:
 		return sync_file_ioctl_fence_info(sync_file, arg);
 
 	default:
diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
index a0cf357..7de5d6a 100644
--- a/drivers/staging/android/uapi/sync.h
+++ b/drivers/staging/android/uapi/sync.h
@@ -16,14 +16,18 @@
 
 /**
  * struct sync_merge_data - data passed to merge ioctl
- * @fd2:	file descriptor of second fence
  * @name:	name of new fence
+ * @fd2:	file descriptor of second fence
  * @fence:	returns the fd of the new fence to userspace
+ * @flags:	merge_data flags
+ * @pad:	padding for 64-bit alignment, should always be zero
  */
 struct sync_merge_data {
-	__s32	fd2; /* fd of second fence */
 	char	name[32]; /* name of new fence */
+	__s32	fd2; /* fd of second fence */
 	__s32	fence; /* fd on newly created fence */
+	__u32	flags;
+	__u32	pad;
 };
 
 /**
@@ -31,42 +35,54 @@ struct sync_merge_data {
  * @obj_name:		name of parent sync_timeline
  * @driver_name:	name of driver implementing the parent
  * @status:		status of the fence 0:active 1:signaled <0:error
+ * @flags:		fence_info flags
  * @timestamp_ns:	timestamp of status change in nanoseconds
  */
 struct sync_fence_info {
 	char	obj_name[32];
 	char	driver_name[32];
 	__s32	status;
+	__u32	flags;
 	__u64	timestamp_ns;
 };
 
 /**
  * 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
- * @sync_fence_info: array of sync_fence_info for every fence in the sync_file
+ * @flags:	sync_file_info flags
+ * @num_fences	number of fences in the sync_file
+ * @pad:	padding for 64-bit alignment, should always be zero
+ * @sync_fence_info: pointer to array of structs sync_fence_info with all
+ *		 fences in the sync_file
  */
 struct sync_file_info {
-	__u32	len;
 	char	name[32];
 	__s32	status;
+	__u32	flags;
+	__u32	num_fences;
+	__u32	pad;
 
-	__u8	sync_fence_info[0];
+	__u64	sync_fence_info;
 };
 
 #define SYNC_IOC_MAGIC		'>'
 
 /**
+ * Opcodes  0, 1 and 2 were burned during a API change to avoid users of the
+ * old API to get weird errors when trying to handling sync_files. The API
+ * change happened during the de-stage of the Sync Framework when there was
+ * no upstream users available.
+ */
+
+/**
  * DOC: SYNC_IOC_MERGE - merge two fences
  *
  * Takes a struct sync_merge_data.  Creates a new fence containing copies of
  * the sync_pts in both the calling fd and sync_merge_data.fd2.  Returns the
  * new fence's fd in sync_merge_data.fence
  */
-#define SYNC_IOC_MERGE		_IOWR(SYNC_IOC_MAGIC, 1, struct sync_merge_data)
+#define SYNC_IOC_MERGE		_IOWR(SYNC_IOC_MAGIC, 3, struct sync_merge_data)
 
 /**
  * DOC: SYNC_IOC_FENCE_INFO - get detailed information on a fence
@@ -79,6 +95,6 @@ struct sync_file_info {
  * pt_info is a buffer containing sync_pt_infos for every sync_pt in the fence.
  * To iterate over the sync_pt_infos, use the sync_pt_info.len field.
  */
-#define SYNC_IOC_FENCE_INFO	_IOWR(SYNC_IOC_MAGIC, 2, struct sync_file_info)
+#define SYNC_IOC_FILE_INFO	_IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
 
 #endif /* _UAPI_LINUX_SYNC_H */
-- 
2.5.5