Re: [PATCH v3 1/6] drm: add DRM_SET_NAME ioctl

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Hi Dmitry,

Le 23/09/2024 à 12:28, Dmitry Osipenko a écrit :
On 9/20/24 12:06, Pierre-Eric Pelloux-Prayer wrote:
Giving the opportunity to userspace to associate a free-form
name with a drm_file struct is helpful for tracking and debugging.

This is similar to the existing DMA_BUF_SET_NAME ioctl.

Access to name is protected by a mutex, and the 'clients' debugfs
file has been updated to print it.

Userspace MR to use this ioctl:
    https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1428

The string passed by userspace is filtered a bit, to avoid messing
output when it's going to be printed (in dmesg, fdinfo, etc):
   * all chars failing isgraph() are replaced by '-'
   * if a 0-length string is passed the name is cleared

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@xxxxxxx>
---
  drivers/gpu/drm/drm_debugfs.c | 12 ++++++---
  drivers/gpu/drm/drm_file.c    |  5 ++++
  drivers/gpu/drm/drm_ioctl.c   | 48 +++++++++++++++++++++++++++++++++++
  include/drm/drm_file.h        |  9 +++++++
  include/uapi/drm/drm.h        | 17 +++++++++++++
  5 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 6b239a24f1df..482e71160544 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -78,12 +78,13 @@ static int drm_clients_info(struct seq_file *m, void *data)
  	kuid_t uid;
seq_printf(m,
-		   "%20s %5s %3s master a %5s %10s\n",
+		   "%20s %5s %3s master a %5s %10s %20s\n",
  		   "command",
  		   "tgid",
  		   "dev",
  		   "uid",
-		   "magic");
+		   "magic",
+		   "name");
/* dev->filelist is sorted youngest first, but we want to present
  	 * oldest first (i.e. kernel, servers, clients), so walk backwardss.
@@ -94,19 +95,22 @@ static int drm_clients_info(struct seq_file *m, void *data)
  		struct task_struct *task;
  		struct pid *pid;
+ mutex_lock(&priv->name_lock);
  		rcu_read_lock(); /* Locks priv->pid and pid_task()->comm! */
  		pid = rcu_dereference(priv->pid);
  		task = pid_task(pid, PIDTYPE_TGID);
  		uid = task ? __task_cred(task)->euid : GLOBAL_ROOT_UID;
-		seq_printf(m, "%20s %5d %3d   %c    %c %5d %10u\n",
+		seq_printf(m, "%20s %5d %3d   %c    %c %5d %10u %20s\n",
  			   task ? task->comm : "<unknown>",
  			   pid_vnr(pid),
  			   priv->minor->index,
  			   is_current_master ? 'y' : 'n',
  			   priv->authenticated ? 'y' : 'n',
  			   from_kuid_munged(seq_user_ns(m), uid),
-			   priv->magic);
+			   priv->magic,
+			   priv->name ?: "");

There should be a default name similar to task->comm, like "<undefined>"
when not set. Perhaps also set name to task->comm by default.

Honestly I don't see much value in printing "<undefined>" or any other default value (+ task->comm is already printed above).


  		rcu_read_unlock();
+		mutex_unlock(&priv->name_lock);
  	}
  	mutex_unlock(&dev->filelist_mutex);
  	return 0;
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 01fde94fe2a9..e9dd0e90a1f9 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -158,6 +158,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
spin_lock_init(&file->master_lookup_lock);
  	mutex_init(&file->event_read_lock);
+	mutex_init(&file->name_lock);
if (drm_core_check_feature(dev, DRIVER_GEM))
  		drm_gem_open(dev, file);
@@ -259,6 +260,10 @@ void drm_file_free(struct drm_file *file)
  	WARN_ON(!list_empty(&file->event_list));
put_pid(rcu_access_pointer(file->pid));
+
+	mutex_destroy(&file->name_lock);
+	kfree(file->name);
+
  	kfree(file);
  }
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 51f39912866f..46dadbd1bb35 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -540,6 +540,52 @@ int drm_version(struct drm_device *dev, void *data,
  	return err;
  }
+static int drm_set_name(struct drm_device *dev, void *data,
+			struct drm_file *file_priv)
+{
+	struct drm_set_name *name = data;
+	void __user *user_ptr;
+	char *new_name;
+	size_t i, len;
+
+	if (name->name_len > DRM_NAME_MAX_LEN)
+		return -EINVAL;
+
+	user_ptr = u64_to_user_ptr(name->name);
+
+	new_name = memdup_user_nul(user_ptr, name->name_len);
+	if (IS_ERR(new_name))
+		return PTR_ERR(new_name);
+
+	len = strlen(new_name);

strnlen

memdup_user_nul returns a NUL-terminated string so I don't see much need for using strnlen.


+	if (len != name->name_len) {
+		kfree(new_name);
+		return -EINVAL;
+	}
+
+	/*
+	 * Filter out control char / spaces / new lines etc in the name
+	 * since it's going to be used in dmesg or fdinfo's output.
+	 */
+	for (i = 0; i < len; i++) {
+		if (!isgraph(new_name[i]))
+			new_name[i] = '-';
+	}
+
+	mutex_lock(&file_priv->name_lock);
+	kfree(file_priv->name);
+	if (len > 0) {
+		file_priv->name = new_name;
+	} else {
+		kfree(new_name);
+		file_priv->name = NULL;
+	}
+	mutex_unlock(&file_priv->name_lock);
+
+	return 0;
+}
+
  static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
  {
  	/* ROOT_ONLY is only for CAP_SYS_ADMIN */
@@ -610,6 +656,8 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
  	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_HANDLE_TO_FD, drm_prime_handle_to_fd_ioctl, DRM_RENDER_ALLOW),
  	DRM_IOCTL_DEF(DRM_IOCTL_PRIME_FD_TO_HANDLE, drm_prime_fd_to_handle_ioctl, DRM_RENDER_ALLOW),
+ DRM_IOCTL_DEF(DRM_IOCTL_SET_NAME, drm_set_name, DRM_RENDER_ALLOW),
+
  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETPLANERESOURCES, drm_mode_getplane_res, 0),
  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETCRTC, drm_mode_getcrtc, 0),
  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_SETCRTC, drm_mode_setcrtc, DRM_MASTER),
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 8c0030c77308..df26eee8f79c 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -388,6 +388,15 @@ struct drm_file {
  	 * Per-file buffer caches used by the PRIME buffer sharing code.
  	 */
  	struct drm_prime_file_private prime;
+
+	/**
+	 * @name:
+	 *
+	 * Userspace-provided name; useful for accounting and debugging.
+	 */
+	const char *name;

I'd make the "name" string static, i.e. char name[DRM_NAME_MAX_LEN + 1].
That will prevent pointer deref troubles and no additional MM code
bloating will be needed.


Sure, I can do that if others prefer this way too.


+	/** @name_lock: Protects @name. */
+	struct mutex name_lock;

And then this lock isn't strictly needed anymore and can be removed if
"name" string is static.

The locking also prevents concurrent modification.


  };
/**
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 16122819edfe..f5e92e4f909b 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -1024,6 +1024,13 @@ struct drm_crtc_queue_sequence {
  	__u64 user_data;	/* user data passed to event */
  };
+#define DRM_NAME_MAX_LEN 64

What about 63, to align data size to 64 bytes including the NULL byte.

Same as "const char *name;" vs "char name[...]": I don't mind updating the code as long as there's a consensus.


+struct drm_set_name {

drm_set_name sounds very generic, IMO. Maybe drm_context_set_name?

drm_client_set_name?
(since other places use client, like drm_clients_info())



+	__u64 name_len;
+	__u64 name;
+};
+
+
  #if defined(__cplusplus)
  }
  #endif
@@ -1288,6 +1295,16 @@ extern "C" {
   */
  #define DRM_IOCTL_MODE_CLOSEFB		DRM_IOWR(0xD0, struct drm_mode_closefb)
+/**
+ * DRM_IOCTL_SET_NAME - Attach a name to a drm_file
+ *
+ * This ioctl is similar to DMA_BUF_SET_NAME - it allows for easier tracking
+ * and debugging.

Don't refer to DMA_BUF_SET_NAME, explain what DRM_IOCTL_SET_NAME
actually do. Tell that it sets the DRM context name and that chars are
filtered.


OK, I'll update based on your suggestion.

Thanks,
Pierre-Eric



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