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

[Klaus Jensen <its@irrelevant.dk>]

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On Nov  9 13:29, Markus Armbruster wrote:
> 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?
> 

Makes total sense. hw/nvme has traditionally used int return values, but
I definitely agree with your argument.

I'll fix that up (and probably do this across all of hw/nvme for
consistency).

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