[PATCH 3/6] tap: Cast TAP_BUF_BYTES - ETH_MAX_MTU to ssize_t, not TAP_BUF_BYTES

Given that we're comparing against 'n', which is signed, we cast TAP_BUF_BYTES to ssize_t so that the maximum buffer usage, calculated as the difference between TAP_BUF_BYTES and ETH_MAX_MTU, will also be signed. This doesn't necessarily happen on 32-bit architectures, though. On armhf and i686, clang-tidy 18.1.8 and 19.1.2 report: /home/pi/passt/tap.c:1087:16: error: comparison of integers of different signs: 'ssize_t' (aka 'int') and 'unsigned int' [clang-diagnostic-sign-compare,-warnings-as-errors] 1087 | for (n = 0; n <= (ssize_t)TAP_BUF_BYTES - ETH_MAX_MTU; n += len) { | ~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ cast the whole difference to ssize_t, as we know it's going to be positive anyway, instead of relying on that side effect. Signed-off-by: Stefano Brivio --- tap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tap.c b/tap.c index f638f2c..a3ba958 100644 --- a/tap.c +++ b/tap.c @@ -1084,7 +1084,7 @@ static void tap_pasta_input(struct ctx *c, const struct timespec *now) tap_flush_pools(); - for (n = 0; n <= (ssize_t)TAP_BUF_BYTES - ETH_MAX_MTU; n += len) { + for (n = 0; n <= (ssize_t)(TAP_BUF_BYTES - ETH_MAX_MTU); n += len) { len = read(c->fd_tap, pkt_buf + n, ETH_MAX_MTU); if (len == 0) { -- 2.43.0