Re: [PATCH v2 1/3] drm: add DRM_SET_NAME ioctl

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Le 16/09/2024 à 16:35, Tvrtko Ursulin a écrit :

On 16/09/2024 14:32, 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   | 42 +++++++++++++++++++++++++++++++++++
  include/drm/drm_file.h        |  9 ++++++++
  include/uapi/drm/drm.h        | 14 ++++++++++++
  5 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 6b239a24f1df..b7492225ae88 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 ? priv->name : "");
          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..b7d7bede0ab3 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -540,6 +540,46 @@ 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_ptr;

__user as kernel test robot reminds us.

Fixed in v3.


+    char *new_name;
+    size_t i, len;
+
+    if (name->name_len >= NAME_MAX)
+        return -EINVAL;

Maybe it is a bit unsubstantiated, but I am leaning towards a feeling of lets define own smaller limit, like dma-buf does. If 32 is deemed too restrictive make it larger but 255 feels unnecessary. But I don't feel to strongly about this so if people insist we need the names this long then so be it.

v3 has "#define DRM_NAME_MAX_LEN       64".


+
+    user_ptr = u64_to_user_ptr(name->name);
+
+    new_name = memdup_user_nul(user_ptr, name->name_len);
+

Nit: I'd zap this blank line since it is breaking a logical group.

Done in v3.


+    if (IS_ERR(new_name))
+        return PTR_ERR(new_name);
+
+    /* Filter out control char / spaces / new lines etc in the name
+     * since it's going to be used in dmesg or fdinfo's output.
+     */

Nit: Preferred kernel style for multi-line comments is:

/*
  * Comment
  */

Unless amdgpu preferes to stick with the above. I think I've seen both used so don't know.

Done in v3.


+    len = strlen(new_name);

Made me think if it is worth cross-checking against name->name_len and reject on mismatch? Probably yes.

Added to v3.


+    for (i = 0; i < len; i++) {
+        if (!isgraph(new_name[i]))
+            new_name[i] = '-';
+    }

For completeness, alternative is to -EINVAL it. I have no strong opinions either way.

For now I've kept the filtering approach and added a comment about it in include/uapi/drm/drm.h.


+
+    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;

FWIW you could not bother allocating new_file in this case.

I've kept the code as-is, I kind of prefer it done the way it is.

Thanks for your review,
Pierre-Eric


Regards,

Tvrtko

+    }
+    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 +650,8 @@ 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;
+    /** @name_lock: Protects @name. */
+    struct mutex name_lock;
  };
  /**
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 16122819edfe..fc62bb21f79e 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -1024,6 +1024,12 @@ struct drm_crtc_queue_sequence {
      __u64 user_data;    /* user data passed to event */
  };
+struct drm_set_name {
+    __u64 name_len;
+    __u64 name;
+};
+
+
  #if defined(__cplusplus)
  }
  #endif
@@ -1288,6 +1294,14 @@ 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.
+ */
+#define DRM_IOCTL_SET_NAME        DRM_IOWR(0xD1, struct drm_set_name)
+
  /*
   * Device specific ioctls should only be in their respective headers
   * The device specific ioctl range is from 0x40 to 0x9f.



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