Re: [PATCH 1/2] hw/nvme: fix incorrect use of errp/local_err

[Markus Armbruster <armbru@redhat.com>]

Klaus Jensen <its@irrelevant.dk> writes:

> From: Klaus Jensen <k.jensen@samsung.com>
>
> Make nvme_check_constraints() return an int and fix incorrect use of
> errp/local_err.
>
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> ---
>  hw/nvme/ctrl.c | 48 +++++++++++++++++++++++-------------------------
>  1 file changed, 23 insertions(+), 25 deletions(-)
>
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index ac3885ce5079..4cc6ae753295 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -7035,7 +7035,7 @@ static const MemoryRegionOps nvme_cmb_ops = {
>      },
>  };
>  
> -static void nvme_check_constraints(NvmeCtrl *n, Error **errp)
> +static int nvme_check_params(NvmeCtrl *n, Error **errp)

I prefer bool true on success, false on failure.  I use int only when it
lets me return additional information, such as a non-negative value on
success, or a negative error code on failure.  nvme_init_pci() is an
example of the latter (although its caller doesn't care).

Local consistency with nvme_init_subsys() is desirable.  You could
convert it to bool, along with nvme_init_pci().  Or you keep all three
int.  Up to you.

>  {
>      NvmeParams *params = &n->params;
>  
> @@ -7049,38 +7049,38 @@ static void nvme_check_constraints(NvmeCtrl *n, Error **errp)
>      if (n->namespace.blkconf.blk && n->subsys) {
>          error_setg(errp, "subsystem support is unavailable with legacy "
>                     "namespace ('drive' property)");
> -        return;
> +        return -1;
>      }
>  
>      if (params->max_ioqpairs < 1 ||
>          params->max_ioqpairs > NVME_MAX_IOQPAIRS) {
>          error_setg(errp, "max_ioqpairs must be between 1 and %d",
>                     NVME_MAX_IOQPAIRS);
> -        return;
> +        return -1;
>      }
>  
>      if (params->msix_qsize < 1 ||
>          params->msix_qsize > PCI_MSIX_FLAGS_QSIZE + 1) {
>          error_setg(errp, "msix_qsize must be between 1 and %d",
>                     PCI_MSIX_FLAGS_QSIZE + 1);
> -        return;
> +        return -1;
>      }
>  
>      if (!params->serial) {
>          error_setg(errp, "serial property not set");
> -        return;
> +        return -1;
>      }
>  
>      if (n->pmr.dev) {
>          if (host_memory_backend_is_mapped(n->pmr.dev)) {
>              error_setg(errp, "can't use already busy memdev: %s",
>                         object_get_canonical_path_component(OBJECT(n->pmr.dev)));
> -            return;
> +            return -1;
>          }
>  
>          if (!is_power_of_2(n->pmr.dev->size)) {
>              error_setg(errp, "pmr backend size needs to be power of 2 in size");
> -            return;
> +            return -1;
>          }
>  
>          host_memory_backend_set_mapped(n->pmr.dev, true);
> @@ -7089,64 +7089,64 @@ static void nvme_check_constraints(NvmeCtrl *n, Error **errp)
>      if (n->params.zasl > n->params.mdts) {
>          error_setg(errp, "zoned.zasl (Zone Append Size Limit) must be less "
>                     "than or equal to mdts (Maximum Data Transfer Size)");
> -        return;
> +        return -1;
>      }
>  
>      if (!n->params.vsl) {
>          error_setg(errp, "vsl must be non-zero");
> -        return;
> +        return -1;
>      }
>  
>      if (params->sriov_max_vfs) {
>          if (!n->subsys) {
>              error_setg(errp, "subsystem is required for the use of SR-IOV");
> -            return;
> +            return -1;
>          }
>  
>          if (params->sriov_max_vfs > NVME_MAX_VFS) {
>              error_setg(errp, "sriov_max_vfs must be between 0 and %d",
>                         NVME_MAX_VFS);
> -            return;
> +            return -1;
>          }
>  
>          if (params->cmb_size_mb) {
>              error_setg(errp, "CMB is not supported with SR-IOV");
> -            return;
> +            return -1;
>          }
>  
>          if (n->pmr.dev) {
>              error_setg(errp, "PMR is not supported with SR-IOV");
> -            return;
> +            return -1;
>          }
>  
>          if (!params->sriov_vq_flexible || !params->sriov_vi_flexible) {
>              error_setg(errp, "both sriov_vq_flexible and sriov_vi_flexible"
>                         " must be set for the use of SR-IOV");
> -            return;
> +            return -1;
>          }
>  
>          if (params->sriov_vq_flexible < params->sriov_max_vfs * 2) {
>              error_setg(errp, "sriov_vq_flexible must be greater than or equal"
>                         " to %d (sriov_max_vfs * 2)", params->sriov_max_vfs * 2);
> -            return;
> +            return -1;
>          }
>  
>          if (params->max_ioqpairs < params->sriov_vq_flexible + 2) {
>              error_setg(errp, "(max_ioqpairs - sriov_vq_flexible) must be"
>                         " greater than or equal to 2");
> -            return;
> +            return -1;
>          }
>  
>          if (params->sriov_vi_flexible < params->sriov_max_vfs) {
>              error_setg(errp, "sriov_vi_flexible must be greater than or equal"
>                         " to %d (sriov_max_vfs)", params->sriov_max_vfs);
> -            return;
> +            return -1;
>          }
>  
>          if (params->msix_qsize < params->sriov_vi_flexible + 1) {
>              error_setg(errp, "(msix_qsize - sriov_vi_flexible) must be"
>                         " greater than or equal to 1");
> -            return;
> +            return -1;
>          }
>  
>          if (params->sriov_max_vi_per_vf &&
> @@ -7154,7 +7154,7 @@ static void nvme_check_constraints(NvmeCtrl *n, Error **errp)
>              error_setg(errp, "sriov_max_vi_per_vf must meet:"
>                         " (sriov_max_vi_per_vf - 1) %% %d == 0 and"
>                         " sriov_max_vi_per_vf >= 1", NVME_VF_RES_GRANULARITY);
> -            return;
> +            return -1;
>          }
>  
>          if (params->sriov_max_vq_per_vf &&
> @@ -7163,9 +7163,11 @@ static void nvme_check_constraints(NvmeCtrl *n, Error **errp)
>              error_setg(errp, "sriov_max_vq_per_vf must meet:"
>                         " (sriov_max_vq_per_vf - 1) %% %d == 0 and"
>                         " sriov_max_vq_per_vf >= 2", NVME_VF_RES_GRANULARITY);
> -            return;
> +            return -1;
>          }
>      }
> +
> +    return 0;
>  }
>  
>  static void nvme_init_state(NvmeCtrl *n)
> @@ -7564,7 +7566,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>  {
>      NvmeCtrl *n = NVME(pci_dev);
>      NvmeNamespace *ns;
> -    Error *local_err = NULL;
>      NvmeCtrl *pn = NVME(pcie_sriov_get_pf(pci_dev));
>  
>      if (pci_is_vf(pci_dev)) {
> @@ -7576,9 +7577,7 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>          n->subsys = pn->subsys;
>      }
>  
> -    nvme_check_constraints(n, &local_err);
> -    if (local_err) {
> -        error_propagate(errp, local_err);
> +    if (nvme_check_params(n, errp)) {

If you stick to int, then please use

       if (nvme_check_params(n, errp) < 0) {

Here's why.

A bool-valued function that returns false on error we check like

       if (!foo()) {

A pointer-valued function that returns null on error we also check like

       if (!foo()) {

In both cases, convention makes it obvious we're testing for failure.

If you check an int-valued function that returns negative on error like

       if (foo() < 0) {

it's again obvious.

However, if you exploit the fact that it returns zero on success in the
check like

       if (foo()) {

then convention is of no help to readers.  They need to look up what
foo() returns to see whether this is checking for success or for
failure.

Makes sense?

>          return;
>      }
>  
> @@ -7586,7 +7585,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
>                &pci_dev->qdev, n->parent_obj.qdev.id);
>  
>      if (nvme_init_subsys(n, errp)) {
> -        error_propagate(errp, local_err);
>          return;
>      }
>      nvme_init_state(n);