From 53628efbc8aa7a7ab5354d24b971f4d69452151d Mon Sep 17 00:00:00 2001 From: "Daniel P. Berrange" Date: Thu, 31 Mar 2016 16:29:27 +0100 Subject: [PATCH] char: fix broken EAGAIN retry on OS-X due to errno clobbering Some of the chardev I/O paths really want to write the complete data buffer even though the channel is in non-blocking mode. To achieve this they look for EAGAIN and g_usleep() for 100ms. Unfortunately the code is set to check errno == EAGAIN a second time, after the g_usleep() call has completed. On OS-X at least, g_usleep clobbers errno to ETIMEDOUT, causing the retry to be skipped. This failure to retry means the full data isn't written to the chardev backend, which causes various failures including making the tests/ahci-test qtest hang. Rather than playing games trying to reset errno just simplify the code to use a goto to retry instead of a a loop. Signed-off-by: Daniel P. Berrange Message-Id: <1459438168-8146-2-git-send-email-berrange@redhat.com> Signed-off-by: Paolo Bonzini --- qemu-char.c | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-) diff --git a/qemu-char.c b/qemu-char.c index 270819aec3..93fd7333f3 100644 --- a/qemu-char.c +++ b/qemu-char.c @@ -225,12 +225,12 @@ static void qemu_chr_fe_write_log(CharDriverState *s, } while (done < len) { - do { - ret = write(s->logfd, buf + done, len - done); - if (ret == -1 && errno == EAGAIN) { - g_usleep(100); - } - } while (ret == -1 && errno == EAGAIN); + retry: + ret = write(s->logfd, buf + done, len - done); + if (ret == -1 && errno == EAGAIN) { + g_usleep(100); + goto retry; + } if (ret <= 0) { return; @@ -246,12 +246,12 @@ static int qemu_chr_fe_write_buffer(CharDriverState *s, const uint8_t *buf, int qemu_mutex_lock(&s->chr_write_lock); while (*offset < len) { - do { - res = s->chr_write(s, buf + *offset, len - *offset); - if (res == -1 && errno == EAGAIN) { - g_usleep(100); - } - } while (res == -1 && errno == EAGAIN); + retry: + res = s->chr_write(s, buf + *offset, len - *offset); + if (res < 0 && errno == EAGAIN) { + g_usleep(100); + goto retry; + } if (res <= 0) { break; @@ -333,12 +333,12 @@ int qemu_chr_fe_read_all(CharDriverState *s, uint8_t *buf, int len) } while (offset < len) { - do { - res = s->chr_sync_read(s, buf + offset, len - offset); - if (res == -1 && errno == EAGAIN) { - g_usleep(100); - } - } while (res == -1 && errno == EAGAIN); + retry: + res = s->chr_sync_read(s, buf + offset, len - offset); + if (res == -1 && errno == EAGAIN) { + g_usleep(100); + goto retry; + } if (res == 0) { break;