On July 3, 2018 7:00 AM, Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> wrote:
> The MTU is negotiated automatically to the maximum value possible but
> it doesn't really matter with WriteValue and ReadValue since they will
> fragment and reassemble the data automatically, with Acquire* you will
> get a file description which you can use to read or write.
The characteristic that I've implemented pulls data from a buffer that is larger than the max value length, so I use the MTU size to determine how many bytes have been read. L2CAP CoC would probably be a better way to do this, but I'm working with platforms that don't support it, unfortunately :-(
> may impact other profiles, so the only option I see here is to have a
> setting in the main.conf saying what is the preferred MTU for
> GATT/ATT [...]
I like this idea. I've attached a patch below that implements this.
Thanks for the suggestions - really helpful.
- dk
diff --git a/src/device.c b/src/device.c
index 4f1af7012..75340cabe 100644
--- a/src/device.c
+++ b/src/device.c
@@ -4986,7 +4986,7 @@ bool device_attach_att(struct btd_device *dev, GIOChannel *io)
}
}
- dev->att_mtu = MIN(mtu, BT_ATT_MAX_LE_MTU);
+ dev->att_mtu = MIN(mtu, main_opts.gatt_max_le_mtu);
attrib = g_attrib_new(io,
cid == ATT_CID ? BT_ATT_DEFAULT_LE_MTU : dev->att_mtu,
false);
diff --git a/src/hcid.h b/src/hcid.h
index 2c2b89d9c..bcb077dde 100644
--- a/src/hcid.h
+++ b/src/hcid.h
@@ -54,6 +54,7 @@ struct main_opts {
bt_mode_t mode;
bt_gatt_cache_t gatt_cache;
+ uint16_t gatt_max_le_mtu;
uint8_t min_enc_key_size;
};
diff --git a/src/main.c b/src/main.c
index 7e6af42cd..8ddd4875f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -50,6 +50,7 @@
#include "log.h"
#include "backtrace.h"
+#include "shared/att-types.h"
#include "lib/uuid.h"
#include "hcid.h"
#include "sdpd.h"
@@ -104,6 +105,7 @@ static const char *policy_options[] = {
static const char *gatt_options[] = {
"Cache",
"MinEncKeySize",
+ "MaxLeMtu",
NULL
};
@@ -419,6 +421,18 @@ static void parse_config(GKeyFile *config)
if (val >=7 && val <= 16)
main_opts.min_enc_key_size = val;
}
+
+ val = g_key_file_get_integer(config, "GATT",
+ "MaxLeMtu", &err);
+ if (err) {
+ g_clear_error(&err);
+ } else {
+ /* Ensure the mtu is within a valid range. */
+ val = MIN(val, BT_ATT_MAX_LE_MTU);
+ val = MAX(val, BT_ATT_DEFAULT_LE_MTU);
+ DBG("gatt_max_le_mtu=%d", val);
+ main_opts.gatt_max_le_mtu = val;
+ }
}
static void init_defaults(void)
@@ -442,6 +456,8 @@ static void init_defaults(void)
main_opts.did_vendor = 0x1d6b; /* Linux Foundation */
main_opts.did_product = 0x0246; /* BlueZ */
main_opts.did_version = (major << 8 | minor);
+
+ main_opts.gatt_max_le_mtu = BT_ATT_MAX_LE_MTU;
}
static void log_handler(const gchar *log_domain, GLogLevelFlags log_level,
diff --git a/src/main.conf b/src/main.conf
index cbae32ec5..a22d685b2 100644
--- a/src/main.conf
+++ b/src/main.conf
@@ -82,6 +82,11 @@
# Defaults to 0
# MinEncKeySize = 0
+# Maximum MTU size.
+# Possible values: 23-517
+# Defaults to 517
+# MaxLeMtu = 517
+
[Policy]
#
# The ReconnectUUIDs defines the set of remote services that should try
--
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