bpftool: Fix spurious batch file read error

do_batch() checks errno after the read loop to detect read failures,
but fgets() does not clear errno on success, so a stale errno left by
a previously executed command (e.g. map dump's EBADF from a double
close) makes bpftool report a batch file read failure and exit with an
error even though every command succeeded.

Clear errno before each fgets() call, so the post-loop check only
sees the outcome of the last read: zero on success or EOF, E2BIG for
an overlong line, and a genuine errno when fgets() fails.

Since errno is now reset before every read in batch mode, drop the
USE_LIBCAP errno reset in main() that existed only to keep errno clean
for the batch mode.

Fixes: 71bb428fe2c1 ("tools: bpf: add bpftool")
Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260824092657.1789956-2-chenyuan_fl@163.com

0 files changed, 0 insertions, 0 deletions