First, follow common recommendations to avoid error propagation:
add return value.

Second, keep NetdevTapOptions related logic in tap.c, and make
tap_set_sndbuf a simple system call wrapper, more like other functions
in tap-linux.c

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 net/tap-bsd.c     |  3 ++-
 net/tap-linux.c   | 19 +++++--------------
 net/tap-solaris.c |  3 ++-
 net/tap-stub.c    |  3 ++-
 net/tap.c         | 10 +++++++---
 net/tap_int.h     |  4 +---
 6 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/net/tap-bsd.c b/net/tap-bsd.c
index b4c84441ba..3bfc1cc577 100644
--- a/net/tap-bsd.c
+++ b/net/tap-bsd.c
@@ -198,8 +198,9 @@ error:
 }
 #endif /* __FreeBSD__ */
 
-void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp)
+bool tap_set_sndbuf(int fd, int sndbuf, Error **errp)
 {
+    return true;
 }
 
 int tap_probe_vnet_hdr(int fd, Error **errp)
diff --git a/net/tap-linux.c b/net/tap-linux.c
index 22ec2f45d2..c46f488c08 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -138,23 +138,14 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
  * Ethernet NICs generally have txqueuelen=1000, so 1Mb is
  * a good value, given a 1500 byte MTU.
  */
-#define TAP_DEFAULT_SNDBUF 0
-
-void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp)
+bool tap_set_sndbuf(int fd, int sndbuf, Error **errp)
 {
-    int sndbuf;
-
-    sndbuf = !tap->has_sndbuf       ? TAP_DEFAULT_SNDBUF :
-             tap->sndbuf > INT_MAX  ? INT_MAX :
-             tap->sndbuf;
-
-    if (!sndbuf) {
-        sndbuf = INT_MAX;
-    }
-
-    if (ioctl(fd, TUNSETSNDBUF, &sndbuf) == -1 && tap->has_sndbuf) {
+    if (ioctl(fd, TUNSETSNDBUF, &sndbuf) == -1) {
         error_setg_errno(errp, errno, "TUNSETSNDBUF ioctl failed");
+        return false;
     }
+
+    return true;
 }
 
 int tap_probe_vnet_hdr(int fd, Error **errp)
diff --git a/net/tap-solaris.c b/net/tap-solaris.c
index 51b7830bef..2932c2de39 100644
--- a/net/tap-solaris.c
+++ b/net/tap-solaris.c
@@ -202,8 +202,9 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
     return fd;
 }
 
-void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp)
+bool tap_set_sndbuf(int fd, int sndbuf, Error **errp)
 {
+    return true;
 }
 
 int tap_probe_vnet_hdr(int fd, Error **errp)
diff --git a/net/tap-stub.c b/net/tap-stub.c
index 38673434cb..326e76843e 100644
--- a/net/tap-stub.c
+++ b/net/tap-stub.c
@@ -33,8 +33,9 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
     return -1;
 }
 
-void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp)
+bool tap_set_sndbuf(int fd, int sndbuf, Error **errp)
 {
+    return true;
 }
 
 int tap_probe_vnet_hdr(int fd, Error **errp)
diff --git a/net/tap.c b/net/tap.c
index e023c5f67f..2ffd8c9907 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -690,9 +690,13 @@ static bool net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
     TAPState *s = net_tap_fd_init(peer, model, name, fd, vnet_hdr);
     int vhostfd;
 
-    tap_set_sndbuf(s->fd, tap, &err);
-    if (err) {
-        error_propagate(errp, err);
+    /* 0 means no limit, so set INT_MAX. Same is the default */
+    int sndbuf =
+        (tap->has_sndbuf && tap->sndbuf) ? MIN(tap->sndbuf, INT_MAX) : INT_MAX;
+
+    /* Ignore error when sndbuf was not requested */
+    if (!tap_set_sndbuf(s->fd, sndbuf, tap->has_sndbuf ? errp : NULL)
+            && tap->has_sndbuf) {
         goto failed;
     }
 
diff --git a/net/tap_int.h b/net/tap_int.h
index 8857ff299d..08e4a592a0 100644
--- a/net/tap_int.h
+++ b/net/tap_int.h
@@ -26,14 +26,12 @@
 #ifndef NET_TAP_INT_H
 #define NET_TAP_INT_H
 
-#include "qapi/qapi-types-net.h"
-
 int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
              int vnet_hdr_required, int mq_required, Error **errp);
 
 ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen);
 
-void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp);
+bool tap_set_sndbuf(int fd, int sndbuf, Error **errp);
 int tap_probe_vnet_hdr(int fd, Error **errp);
 int tap_probe_has_ufo(int fd);
 int tap_probe_has_uso(int fd);
-- 
2.48.1