[PATCH 1/3] tty: n_gsm: introduce macro for minimal unit size

From: D. Starke
Date: Fri Oct 21 2022 - 04:46:14 EST


From: Daniel Starke <daniel.starke@xxxxxxxxxxx>

n_gsm has a minimal protocol overhead of 7 bytes. The current code already
checks whether the configured MRU/MTU size is at least one byte more than
this.

Introduce the macro MIN_UNIT_SIZE to make this value more obvious.

Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx>
---
drivers/tty/n_gsm.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 5e516f5cac5a..8e039f2a0427 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -89,6 +89,7 @@ module_param(debug, int, 0600);
*/
#define MAX_MRU 1500
#define MAX_MTU 1500
+#define MIN_UNIT_SIZE 8
/* SOF, ADDR, CTRL, LEN1, LEN2, ..., FCS, EOF */
#define PROT_OVERHEAD 7
#define GSM_NET_TX_TIMEOUT (HZ*10)
@@ -2712,7 +2713,9 @@ static int gsm_config(struct gsm_mux *gsm, struct gsm_config *c)
if ((c->adaption != 1 && c->adaption != 2) || c->k)
return -EOPNOTSUPP;
/* Check the MRU/MTU range looks sane */
- if (c->mru > MAX_MRU || c->mtu > MAX_MTU || c->mru < 8 || c->mtu < 8)
+ if (c->mru < MIN_UNIT_SIZE || c->mtu < MIN_UNIT_SIZE)
+ return -EINVAL;
+ if (c->mru > MAX_MRU || c->mtu > MAX_MTU)
return -EINVAL;
if (c->n2 > 255)
return -EINVAL;
@@ -3296,7 +3299,7 @@ static int gsm_create_network(struct gsm_dlci *dlci, struct gsm_netconfig *nc)
return -ENOMEM;
}
net->mtu = dlci->gsm->mtu;
- net->min_mtu = 8;
+ net->min_mtu = MIN_UNIT_SIZE;
net->max_mtu = dlci->gsm->mtu;
mux_net = netdev_priv(net);
mux_net->dlci = dlci;
--
2.34.1