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ALSA: seq: oss: Send fragmented SysEx messages immediately

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The recent bug report spotted on the old OSS sequencer code that tries
to combine incoming SysEx messages to a single sequencer event.  This
is good, per se, but it has more demerits:

- The sysex message delivery is delayed until the very last event
- The use of internal buffer forced the serialization

The recent fix in commit 0179488ca9 ("ALSA: seq: oss: Fix races at
processing SysEx messages") addressed the latter, but a better fix is
to handle the sysex messages immediately, i.e. just send each incoming
fragmented sysex message as is.  And this patch implements that.
This resulted in a significant cleanup as well.

Note that the only caller of snd_seq_oss_synth_sysex() is
snd_seq_oss_process_event(), and all its callers dispatch the event
immediately, so we can just put the passed buffer pointer to the event
record to be handled.

Reported-and-tested-by: Kun Hu <huk23@m.fudan.edu.cn>
Link: https://lore.kernel.org/2B7E93E4-B13A-4AE4-8E87-306A8EE9BBB7@m.fudan.edu.cn
Link: https://patch.msgid.link/20241231115523.15796-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2024-12-31 12:55:18 +01:00
parent 41d11d6e1a
commit 20ce9ded8c
2 changed files with 14 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
sound/core/seq/oss/seq_oss_device.h
View File

@ -55,7 +55,6 @@ struct seq_oss_chinfo {
struct seq_oss_synthinfo {
struct snd_seq_oss_arg arg;
struct seq_oss_chinfo *ch;
struct seq_oss_synth_sysex *sysex;
int nr_voices;
int opened;
int is_midi;

80
sound/core/seq/oss/seq_oss_synth.c
View File

@ -26,13 +26,6 @@
* definition of synth info records
*/
/* sysex buffer */
struct seq_oss_synth_sysex {
int len;
int skip;
unsigned char buf[MAX_SYSEX_BUFLEN];
};
/* synth info */
struct seq_oss_synth {
int seq_device;
@ -66,7 +59,6 @@ static struct seq_oss_synth midi_synth_dev = {
};
static DEFINE_SPINLOCK(register_lock);
static DEFINE_MUTEX(sysex_mutex);
/*
* prototypes
@ -319,8 +311,6 @@ snd_seq_oss_synth_cleanup(struct seq_oss_devinfo *dp)
}
snd_use_lock_free(&rec->use_lock);
}
kfree(info->sysex);
info->sysex = NULL;
kfree(info->ch);
info->ch = NULL;
}
@ -396,8 +386,6 @@ snd_seq_oss_synth_reset(struct seq_oss_devinfo *dp, int dev)
info = get_synthinfo_nospec(dp, dev);
if (!info || !info->opened)
return;
if (info->sysex)
info->sysex->len = 0; /* reset sysex */
reset_channels(info);
if (info->is_midi) {
if (midi_synth_dev.opened <= 0)
@ -409,8 +397,6 @@ snd_seq_oss_synth_reset(struct seq_oss_devinfo *dp, int dev)
dp->file_mode) < 0) {
midi_synth_dev.opened--;
info->opened = 0;
kfree(info->sysex);
info->sysex = NULL;
kfree(info->ch);
info->ch = NULL;
}
@ -483,64 +469,26 @@ snd_seq_oss_synth_info(struct seq_oss_devinfo *dp, int dev)
/*
* receive OSS 6 byte sysex packet:
* the full sysex message will be sent if it reaches to the end of data
* (0xff).
* the event is filled and prepared for sending immediately
* (i.e. sysex messages are fragmented)
*/
int
snd_seq_oss_synth_sysex(struct seq_oss_devinfo *dp, int dev, unsigned char *buf, struct snd_seq_event *ev)
{
int i, send;
unsigned char *dest;
struct seq_oss_synth_sysex *sysex;
struct seq_oss_synthinfo *info;
unsigned char *p;
int len = 6;
info = snd_seq_oss_synth_info(dp, dev);
if (!info)
return -ENXIO;
p = memchr(buf, 0xff, 6);
if (p)
len = p - buf + 1;
guard(mutex)(&sysex_mutex);
sysex = info->sysex;
if (sysex == NULL) {
sysex = kzalloc(sizeof(*sysex), GFP_KERNEL);
if (sysex == NULL)
return -ENOMEM;
info->sysex = sysex;
}
send = 0;
dest = sysex->buf + sysex->len;
/* copy 6 byte packet to the buffer */
for (i = 0; i < 6; i++) {
if (buf[i] == 0xff) {
send = 1;
break;
}
dest[i] = buf[i];
sysex->len++;
if (sysex->len >= MAX_SYSEX_BUFLEN) {
sysex->len = 0;
sysex->skip = 1;
break;
}
}
if (sysex->len && send) {
if (sysex->skip) {
sysex->skip = 0;
sysex->len = 0;
return -EINVAL; /* skip */
}
/* copy the data to event record and send it */
ev->flags = SNDRV_SEQ_EVENT_LENGTH_VARIABLE;
if (snd_seq_oss_synth_addr(dp, dev, ev))
return -EINVAL;
ev->data.ext.len = sysex->len;
ev->data.ext.ptr = sysex->buf;
sysex->len = 0;
return 0;
}
return -EINVAL; /* skip */
/* copy the data to event record and send it */
if (snd_seq_oss_synth_addr(dp, dev, ev))
return -EINVAL;
ev->flags = SNDRV_SEQ_EVENT_LENGTH_VARIABLE;
ev->data.ext.len = len;
ev->data.ext.ptr = buf;
return 0;
}
/*