linux-kernel - Re: [PATCH 3/5] iommu: Add return errno rules to ->attach

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Date:   Tue, 13 Sep 2022 13:00:27 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jeff Johnson <quic_jjohnson@...cinc.com>
CC:     <joro@...tes.org>, <suravee.suthikulpanit@....com>,
        <will@...nel.org>, <robin.murphy@....com>, <robdclark@...il.com>,
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Subject: Re: [PATCH 3/5] iommu: Add return errno rules to ->attach_dev ops

Hi Jeff,

On Tue, Sep 13, 2022 at 11:41:35AM -0700, Jeff Johnson wrote:
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index ea30f00dc145..c5d7ec0187c7 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -266,6 +266,17 @@ struct iommu_ops {
> >   /**
> >    * struct iommu_domain_ops - domain specific operations
> >    * @attach_dev: attach an iommu domain to a device
> > + *              Rules of its return errno:
> > + *               EINVAL  - Exclusively, device and domain are incompatible. Must
> > + *                         avoid kernel prints along with this errno. Any EINVAL
> > + *                         returned from kAPIs must be converted to ENODEV if it
> > + *                         is device-specific, or to some other reasonable errno
> > + *                         being listed below
> > + *               ENOMEM  - Out of memory
> > + *               ENOSPC  - No space left on device
> > + *               EBUSY   - Device is attached to a domain and cannot be changed
> > + *               ENODEV  - Device specific errors, not able to be attached
> > + *              <others> - Treated as ENODEV by the caller. Use is discouraged
> 
> It is my understanding that kernel-doc won't preserve your formatting
> without extra directives. See the "Note" after
> <https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#return-values>

Thanks for the review!

Perhaps the following one would work:

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ea30f00dc145..14f078b58e17 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -266,6 +266,17 @@ struct iommu_ops {
 /**
  * struct iommu_domain_ops - domain specific operations
  * @attach_dev: attach an iommu domain to a device
+ *  Return:
+ * * 0         - success
+ * * EINVAL    - Exclusively, device and domain are incompatible. Must avoid
+ *               kernel prints along with this errno. Any EINVAL returned from
+ *               a kAPI must be converted to ENODEV if it is device-specific,
+ *               or to some other reasonable errno being listed below
+ * * ENOMEM    - Out of memory
+ * * ENOSPC    - No space left on device
+ * * EBUSY     - Device is attached to a domain and cannot be changed
+ * * ENODEV    - Device specific errors, not able to be attached
+ * * <others>  - Treated as ENODEV by the caller. Use is discouraged
  * @detach_dev: detach an iommu domain from a device
  * @map: map a physically contiguous memory region to an iommu domain
  * @map_pages: map a physically contiguous set of pages of the same size to