Re: [PATCH v3 3/3] backends/tpm: Propagate vTPM error on migration failure

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jul 02, 2025 at 05:06:52PM +0530, Arun Menon wrote:
> - Use the post_load_with_error() hook to propagate TPM
>   errors.
> - The error object is set if the loading of state fails.
>   It can then be retrieved using QMP command:
>   {"execute" : "query-migrate"}

This is only describing what has been done - good commit messages
should primarily describe why it is being done.

> Buglink: https://issues.redhat.com/browse/RHEL-82826

We shouldn't rely on people reading through the buglink to
learn the 'why' - please summarize the important contextual
info and problem scenario here.

> 
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  backends/tpm/tpm_emulator.c | 39 ++++++++++++++++++++-------------------
>  1 file changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c
> index 4a234ab2c0b19b2604bf0dd8cb5f4540c72a9438..816134d7b4de00a75a3d0b928d160595b17be810 100644
> --- a/backends/tpm/tpm_emulator.c
> +++ b/backends/tpm/tpm_emulator.c
> @@ -819,7 +819,8 @@ static int tpm_emulator_get_state_blobs(TPMEmulator *tpm_emu)
>  static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>                                         uint32_t type,
>                                         TPMSizedBuffer *tsb,
> -                                       uint32_t flags)
> +                                       uint32_t flags,
> +                                       Error **errp)
>  {
>      ssize_t n;
>      ptm_setstate pss;
> @@ -838,17 +839,17 @@ 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_report("tpm-emulator: could not set state blob type %d : %s",
> -                     type, strerror(errno));
> +        error_setg(errp, "tpm-emulator: could not set state blob type %d : %s",
> +                   type, strerror(errno));
>          return -1;
>      }
>  
>      /* now the body */
>      n = qemu_chr_fe_write_all(&tpm_emu->ctrl_chr, tsb->buffer, tsb->size);
>      if (n != tsb->size) {
> -        error_report("tpm-emulator: Writing the stateblob (type %d) "
> -                     "failed; could not write %u bytes, but only %zd",
> -                     type, tsb->size, n);
> +        error_setg(errp, "tpm-emulator: Writing the stateblob (type %d) "
> +                   "failed; could not write %u bytes, but only %zd",
> +                   type, tsb->size, n);
>          return -1;
>      }
>  
> @@ -856,17 +857,17 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>      n = qemu_chr_fe_read_all(&tpm_emu->ctrl_chr,
>                               (uint8_t *)&pss, sizeof(pss.u.resp));
>      if (n != sizeof(pss.u.resp)) {
> -        error_report("tpm-emulator: Reading response from writing stateblob "
> -                     "(type %d) failed; expected %zu bytes, got %zd", type,
> -                     sizeof(pss.u.resp), n);
> +        error_setg(errp, "tpm-emulator: Reading response from writing "
> +                   "stateblob (type %d) failed; expected %zu bytes, "
> +                   "got %zd", type, sizeof(pss.u.resp), n);
>          return -1;
>      }
>  
>      tpm_result = be32_to_cpu(pss.u.resp.tpm_result);
>      if (tpm_result != 0) {
> -        error_report("tpm-emulator: Setting the stateblob (type %d) failed "
> -                     "with a TPM error 0x%x %s", type, tpm_result,
> -                     tpm_emulator_strerror(tpm_result));
> +        error_setg(errp, "tpm-emulator: Setting the stateblob (type %d) "
> +                   "failed with a TPM error 0x%x %s", type, tpm_result,
> +                   tpm_emulator_strerror(tpm_result));
>          return -1;
>      }
>  
> @@ -880,7 +881,7 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
>   *
>   * Returns a negative errno code in case of error.
>   */
> -static int tpm_emulator_set_state_blobs(TPMBackend *tb)
> +static int tpm_emulator_set_state_blobs(TPMBackend *tb, Error **errp)
>  {
>      TPMEmulator *tpm_emu = TPM_EMULATOR(tb);
>      TPMBlobBuffers *state_blobs = &tpm_emu->state_blobs;
> @@ -894,13 +895,13 @@ static int tpm_emulator_set_state_blobs(TPMBackend *tb)
>  
>      if (tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_PERMANENT,
>                                      &state_blobs->permanent,
> -                                    state_blobs->permanent_flags) < 0 ||
> +                                    state_blobs->permanent_flags, errp) < 0 ||
>          tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_VOLATILE,
>                                      &state_blobs->volatil,
> -                                    state_blobs->volatil_flags) < 0 ||
> +                                    state_blobs->volatil_flags, errp) < 0 ||
>          tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_SAVESTATE,
>                                      &state_blobs->savestate,
> -                                    state_blobs->savestate_flags) < 0) {
> +                                    state_blobs->savestate_flags, errp) < 0) {
>          return -EIO;
>      }
>  
> @@ -948,12 +949,12 @@ static void tpm_emulator_vm_state_change(void *opaque, bool running,
>   *
>   * Returns negative errno codes in case of error.
>   */
> -static int tpm_emulator_post_load(void *opaque, int version_id)
> +static int tpm_emulator_post_load(void *opaque, int version_id, Error **errp)
>  {
>      TPMBackend *tb = opaque;
>      int ret;
>  
> -    ret = tpm_emulator_set_state_blobs(tb);
> +    ret = tpm_emulator_set_state_blobs(tb, errp);
>      if (ret < 0) {
>          return ret;
>      }
> @@ -969,7 +970,7 @@ static const VMStateDescription vmstate_tpm_emulator = {
>      .name = "tpm-emulator",
>      .version_id = 0,
>      .pre_save = tpm_emulator_pre_save,
> -    .post_load = tpm_emulator_post_load,
> +    .post_load_with_error = tpm_emulator_post_load,
>      .fields = (const VMStateField[]) {
>          VMSTATE_UINT32(state_blobs.permanent_flags, TPMEmulator),
>          VMSTATE_UINT32(state_blobs.permanent.size, TPMEmulator),
> 
> -- 
> 2.49.0
> 
> 

With regards,
Daniel
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