[alsa-devel] [PATCH - alsa-lib 1/1] Change card/pid get functions to return -ENOSYS if the kernel is too old

[Adam Goode]

When trying to get the pid or card of a client, the get functions will
return -1 if there is no pid or card for a client. Clients have zero or
one of these, so -1 is correct for these cases. But we also need to detect
the case where the kernel cannot tell us if there is a card or pid, so
that userspace can fallback to probing this information in the old way.

Signed-off-by: Adam Goode <agoode at google.com>

diff --git a/src/seq/seq.c b/src/seq/seq.c
index 4405e68..7de1e81 100644
--- a/src/seq/seq.c
+++ b/src/seq/seq.c
@@ -1522,9 +1522,10 @@ int snd_seq_client_info_get_error_bounce(const snd_seq_client_info_t *info)
 }
 
 /**
- * \brief Get the sound card number.
+ * \brief Get the sound card number if the kernel supports this.
  * \param info client_info container
- * \return card number or -1 if value is not available.
+ * \return card number, -1 if there is no card for this client,
+ *  or \c -ENOSYS if the kernel does not have support for this operation
  *
  * Only available for SND_SEQ_KERNEL_CLIENT clients.
  */
@@ -1535,9 +1536,10 @@ int snd_seq_client_info_get_card(const snd_seq_client_info_t *info)
 }
 
 /**
- * \brief Get the owning PID.
+ * \brief Get the owning PID if the kernel supports this.
  * \param info client_info container
- * \return pid or -1 if value is not available.
+ * \return pid, -1 if there is no PID for this client,
+ *  or \c -ENOSYS if the kernel does not have support for this operation
  *
  * Only available for SND_SEQ_USER_CLIENT clients.
  */
diff --git a/src/seq/seq_hw.c b/src/seq/seq_hw.c
index 578ef12..a1d1e4a 100644
--- a/src/seq/seq_hw.c
+++ b/src/seq/seq_hw.c
@@ -102,8 +102,8 @@ static int snd_seq_hw_get_client_info(snd_seq_t *seq, snd_seq_client_info_t * in
 		return -errno;
 	}
 	if (hw->version < SNDRV_PROTOCOL_VERSION(1, 0, 2)) {
-		info->card = -1;
-		info->pid = -1;
+		info->card = -ENOSYS;
+		info->pid = -ENOSYS;
 	}
 	return 0;
 }
@@ -374,8 +374,8 @@ static int snd_seq_hw_query_next_client(snd_seq_t *seq, snd_seq_client_info_t *i
 		return -errno;
 	}
 	if (hw->version < SNDRV_PROTOCOL_VERSION(1, 0, 2)) {
-		info->card = -1;
-		info->pid = -1;
+		info->card = -ENOSYS;
+		info->pid = -ENOSYS;
 	}
 	return 0;
 }
-- 
2.8.0.rc3.226.g39d4020