Re: [PATCH 2/3] tpm_emulator: drop direct use of errno variable

[Stefan Berger <stefanb@linux.ibm.com>]

On 11/6/25 2:41 PM, Vladimir Sementsov-Ogievskiy wrote:
> The code tends to include errno into error messages after
> tpm_util_test_tpmdev() and tpm_emulator_ctrlcmd() calls.
> 
> Both has error paths, where errno is not set, examples:

Both have ...>
> tpm_emulator_ctrlcmd()
>    qemu_chr_fe_write_all()
>      qemu_chr_write()
>        replay_char_write_event_load()
>          ...
>          *res = replay_get_dword();
>          ...
> 
> tpm_util_test_tpmdev()
>    tpm_util_test()
>      tpm_util_request()
>        ...
>        if (n != requestlen) {
>            return -EFAULT;
>        }
>        ...
> 
> Both doesn't document that they set errno.

Both do not ...

> 
> Let's drop these explicit usage of errno. If we need this information,
> it should be added to errp deeper in the stack.

It's not clear to me why this is an actual problem. Is it better to now 
not set this error message?

> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>   backends/tpm/tpm_emulator.c | 44 ++++++++++++++-----------------------
>   1 file changed, 16 insertions(+), 28 deletions(-)
> 
> diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c
> index 24aa18302e..79f3e6b1f2 100644
> --- a/backends/tpm/tpm_emulator.c
> +++ b/backends/tpm/tpm_emulator.c
> @@ -225,8 +225,7 @@ static int tpm_emulator_set_locality(TPMEmulator *tpm_emu, uint8_t locty_number,
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_LOCALITY, &loc,
>                                sizeof(loc), sizeof(loc.u.resp.tpm_result),
>                                sizeof(loc)) < 0) {
> -        error_setg(errp, "tpm-emulator: could not set locality : %s",
> -                   strerror(errno));
> +        error_setg(errp, "tpm-emulator: could not set locality");
>           return -1;
>       }
> 
> @@ -264,7 +263,7 @@ static int tpm_emulator_probe_caps(TPMEmulator *tpm_emu)
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_GET_CAPABILITY, &cap_n, 0,
>                                sizeof(cap_n.u.resp.tpm_result),
>                                sizeof(cap_n)) < 0) {
> -        error_report("tpm-emulator: probing failed : %s", strerror(errno));
> +        error_report("tpm-emulator: probing failed");
>           return -1;
>       }
> 
> @@ -315,8 +314,7 @@ static int tpm_emulator_stop_tpm(TPMBackend *tb, Error **errp)
> 
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_STOP, &res, 0,
>                                sizeof(ptm_res), sizeof(res)) < 0) {
> -        error_setg(errp, "tpm-emulator: Could not stop TPM: %s",
> -                   strerror(errno));
> +        error_setg(errp, "tpm-emulator: Could not stop TPM");
>           return -1;
>       }
> 
> @@ -344,8 +342,7 @@ static int tpm_emulator_lock_storage(TPMEmulator *tpm_emu)
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_LOCK_STORAGE, &pls, sizeof(pls.u.req),
>                                sizeof(pls.u.resp.tpm_result),
>                                sizeof(pls.u.resp)) < 0) {
> -        error_report("tpm-emulator: Could not lock storage within 3 seconds: "
> -                     "%s", strerror(errno));
> +        error_report("tpm-emulator: Could not lock storage within 3 seconds");
>           return -1;
>       }
> 
> @@ -377,8 +374,7 @@ static int tpm_emulator_set_buffer_size(TPMBackend *tb,
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_BUFFERSIZE, &psbs,
>                                sizeof(psbs.u.req), sizeof(psbs.u.resp.tpm_result),
>                                sizeof(psbs.u.resp)) < 0) {
> -        error_setg(errp, "tpm-emulator: Could not set buffer size: %s",
> -                   strerror(errno));
> +        error_setg(errp, "tpm-emulator: Could not set buffer size");
>           return -1;
>       }
> 
> @@ -426,8 +422,7 @@ static int tpm_emulator_startup_tpm_resume(TPMBackend *tb, size_t buffersize,
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_INIT, &init, sizeof(init),
>                                sizeof(init.u.resp.tpm_result),
>                                sizeof(init)) < 0) {
> -        error_setg(errp, "tpm-emulator: could not send INIT: %s",
> -                   strerror(errno));
> +        error_setg(errp, "tpm-emulator: could not send INIT");
>           goto err_exit;
>       }
> 
> @@ -482,8 +477,7 @@ static bool tpm_emulator_get_tpm_established_flag(TPMBackend *tb)
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_GET_TPMESTABLISHED, &est, 0,
>                                sizeof(est) /* always returns resp.bit */,
>                                sizeof(est)) < 0) {
> -        error_report("tpm-emulator: Could not get the TPM established flag: %s",
> -                     strerror(errno));
> +        error_report("tpm-emulator: Could not get the TPM established flag");
>           return false;
>       }
>       trace_tpm_emulator_get_tpm_established_flag(est.u.resp.bit);
> @@ -511,8 +505,7 @@ static int tpm_emulator_reset_tpm_established_flag(TPMBackend *tb,
>                                &reset_est, sizeof(reset_est),
>                                sizeof(reset_est.u.resp.tpm_result),
>                                sizeof(reset_est)) < 0) {
> -        error_report("tpm-emulator: Could not reset the establishment bit: %s",
> -                     strerror(errno));
> +        error_report("tpm-emulator: Could not reset the establishment bit");
>           return -1;
>       }
> 
> @@ -542,8 +535,7 @@ static void tpm_emulator_cancel_cmd(TPMBackend *tb)
>       /* FIXME: make the function non-blocking, or it may block a VCPU */
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_CANCEL_TPM_CMD, &res, 0,
>                                sizeof(ptm_res), sizeof(res)) < 0) {
> -        error_report("tpm-emulator: Could not cancel command: %s",
> -                     strerror(errno));
> +        error_report("tpm-emulator: Could not cancel command: %s");
>       } else if (res != 0) {
>           error_report("tpm-emulator: Failed to cancel TPM: 0x%x",
>                        be32_to_cpu(res));
> @@ -604,8 +596,7 @@ static int tpm_emulator_prepare_data_fd(TPMEmulator *tpm_emu)
> 
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_DATAFD, &res, 0,
>                                sizeof(ptm_res), sizeof(res)) < 0 || res != 0) {
> -        error_report("tpm-emulator: Failed to send CMD_SET_DATAFD: %s",
> -                     strerror(errno));
> +        error_report("tpm-emulator: Failed to send CMD_SET_DATAFD");
>           goto err_exit;
>       }
> 
> @@ -662,8 +653,8 @@ static int tpm_emulator_handle_device_opts(TPMEmulator *tpm_emu, QemuOpts *opts)
>        */
>       if (tpm_util_test_tpmdev(QIO_CHANNEL_SOCKET(tpm_emu->data_ioc)->fd,
>                                &tpm_emu->tpm_version)) {
> -        error_report("'%s' is not emulating TPM device. Error: %s",
> -                      tpm_emu->options->chardev, strerror(errno));
> +        error_report("'%s' is not emulating TPM device.",
> +                      tpm_emu->options->chardev);
>           goto err;
>       }
> 
> @@ -753,8 +744,7 @@ static int tpm_emulator_get_state_blob(TPMEmulator *tpm_emu,
>                                /* always returns up to resp.data */
>                                offsetof(ptm_getstate, u.resp.data),
>                                offsetof(ptm_getstate, u.resp.data)) < 0) {
> -        error_report("tpm-emulator: could not get state blob type %d : %s",
> -                     type, strerror(errno));
> +        error_report("tpm-emulator: could not get state blob type %d", type);
>           return -1;
>       }
> 
> @@ -856,9 +846,8 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>       /* write the header only */
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_STATEBLOB, &pss,
>                                offsetof(ptm_setstate, u.req.data), 0, 0) < 0) {
> -        error_setg_errno(errp, errno,
> -                         "tpm-emulator: could not set state blob type %d",
> -                         type);
> +        error_setg(errp, "tpm-emulator: could not set state blob type %d",
> +                   type);
>           return -1;
>       }
> 
> @@ -1040,8 +1029,7 @@ static void tpm_emulator_shutdown(TPMEmulator *tpm_emu)
> 
>       if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SHUTDOWN, &res, 0,
>                                sizeof(ptm_res), sizeof(res)) < 0) {
> -        error_report("tpm-emulator: Could not cleanly shutdown the TPM: %s",
> -                     strerror(errno));
> +        error_report("tpm-emulator: Could not cleanly shutdown the TPM");
>       } else if (res != 0) {
>           error_report("tpm-emulator: TPM result for shutdown: 0x%x %s",
>                        be32_to_cpu(res), tpm_emulator_strerror(be32_to_cpu(res)));