Message-ID: <CAJHc60z49qAhPkug25Gm-TU_pqgSius7LndkhuEam54ZhKWYMg@mail.gmail.com>
Date: Thu, 8 Jan 2026 13:25:19 -0800
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: David Matlack <dmatlack@...gle.com>
Cc: Alex Williamson <alex@...zbot.org>, Alex Williamson <alex.williamson@...hat.com>, 
	Josh Hilke <jrhilke@...gle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] vfio: selftests: Introduce a sysfs lib

On Wed, Jan 7, 2026 at 2:41 PM David Matlack <dmatlack@...gle.com> wrote:
>
> On 2025-12-10 06:14 PM, Raghavendra Rao Ananta wrote:
> > Introduce a sysfs liibrary to handle the common reads/writes to the
>                     library
>
> > PCI sysfs files, for example, getting the total number of VFs supported
> > by the device via /sys/bus/pci/devices/$BDF/sriov_totalvfs. The library
> > will be used in the upcoming test patch to configure the VFs for a given
> > PF device.
> >
> > Opportunistically, move vfio_pci_get_group_from_dev() to this library as
> > it falls under the same bucket. Rename it to sysfs_get_device_group() to
> > align with other function names.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> > ---
> >  .../selftests/vfio/lib/include/libvfio.h      |   1 +
> >  .../vfio/lib/include/libvfio/sysfs.h          |  16 ++
> >  tools/testing/selftests/vfio/lib/libvfio.mk   |   1 +
> >  tools/testing/selftests/vfio/lib/sysfs.c      | 151 ++++++++++++++++++
> >  .../selftests/vfio/lib/vfio_pci_device.c      |  22 +--
> >  5 files changed, 170 insertions(+), 21 deletions(-)
> >  create mode 100644 tools/testing/selftests/vfio/lib/include/libvfio/sysfs.h
> >  create mode 100644 tools/testing/selftests/vfio/lib/sysfs.c
> >
> > diff --git a/tools/testing/selftests/vfio/lib/include/libvfio.h b/tools/testing/selftests/vfio/lib/include/libvfio.h
> > index 279ddcd701944..bbe1d7616a648 100644
> > --- a/tools/testing/selftests/vfio/lib/include/libvfio.h
> > +++ b/tools/testing/selftests/vfio/lib/include/libvfio.h
> > @@ -5,6 +5,7 @@
> >  #include <libvfio/assert.h>
> >  #include <libvfio/iommu.h>
> >  #include <libvfio/iova_allocator.h>
> > +#include <libvfio/sysfs.h>
> >  #include <libvfio/vfio_pci_device.h>
> >  #include <libvfio/vfio_pci_driver.h>
> >
> > diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/sysfs.h b/tools/testing/selftests/vfio/lib/include/libvfio/sysfs.h
> > new file mode 100644
> > index 0000000000000..1eca6b5cbcfcc
> > --- /dev/null
> > +++ b/tools/testing/selftests/vfio/lib/include/libvfio/sysfs.h
> > @@ -0,0 +1,16 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +#ifndef SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_SYSFS_H
> > +#define SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_SYSFS_H
> > +
> > +int sysfs_get_sriov_totalvfs(const char *bdf);
> > +int sysfs_get_sriov_numvfs(const char *bdf);
> > +void sysfs_set_sriov_numvfs(const char *bdfs, int numvfs);
> > +void sysfs_get_sriov_vf_bdf(const char *pf_bdf, int i, char *out_vf_bdf);
> > +bool sysfs_get_sriov_drivers_autoprobe(const char *bdf);
> > +void sysfs_set_sriov_drivers_autoprobe(const char *bdf, bool val);
> > +void sysfs_bind_driver(const char *bdf, const char *driver);
> > +void sysfs_unbind_driver(const char *bdf, const char *driver);
> > +int sysfs_get_driver(const char *bdf, char *out_driver);
> > +unsigned int sysfs_get_device_group(const char *bdf);
> > +
> > +#endif /* SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_SYSFS_H */
> > diff --git a/tools/testing/selftests/vfio/lib/libvfio.mk b/tools/testing/selftests/vfio/lib/libvfio.mk
> > index 9f47bceed16f4..b7857319c3f1f 100644
> > --- a/tools/testing/selftests/vfio/lib/libvfio.mk
> > +++ b/tools/testing/selftests/vfio/lib/libvfio.mk
> > @@ -6,6 +6,7 @@ LIBVFIO_SRCDIR := $(selfdir)/vfio/lib
> >  LIBVFIO_C := iommu.c
> >  LIBVFIO_C += iova_allocator.c
> >  LIBVFIO_C += libvfio.c
> > +LIBVFIO_C += sysfs.c
> >  LIBVFIO_C += vfio_pci_device.c
> >  LIBVFIO_C += vfio_pci_driver.c
> >
> > diff --git a/tools/testing/selftests/vfio/lib/sysfs.c b/tools/testing/selftests/vfio/lib/sysfs.c
> > new file mode 100644
> > index 0000000000000..5551e8b981075
> > --- /dev/null
> > +++ b/tools/testing/selftests/vfio/lib/sysfs.c
> > @@ -0,0 +1,151 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +#include <fcntl.h>
> > +#include <unistd.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <linux/limits.h>
> > +
> > +#include <libvfio.h>
> > +
> > +static int sysfs_get_val(const char *component, const char *name,
>
> nit: I'm partial to putting the verbs at the end of function names for
> library calls.
>
> e.g.
>
>   vfio_pci_config_read()
>   vfio_pci_config_write()
>   vfio_pci_msi_enable()
>   vfio_pci_msi_disable()
>
> So these would be:
>
>   sysfs_val_set()
>   sysfs_val_get()
>   sysfs_device_val_set()
>   sysfs_device_val_get()
>   sysfs_sriov_numvfs_set()
>   sysfs_sriov_numvfs_get()
>   ...
>
> > +                      const char *file)
> > +{
> > +     char path[PATH_MAX] = {0};
> > +     char buf[32] = {0};
>
> nit: You don't need to zero-initialize these since you only use them
> after they are intitialized below.
>
> > +     int fd;
> > +
> > +     snprintf(path, PATH_MAX, "/sys/bus/pci/%s/%s/%s", component, name, file);
>
> Use the new snprintf_assert() :)
>
> > +     fd = open(path, O_RDONLY);
> > +     if (fd < 0)
> > +             return fd;
> > +
> > +     VFIO_ASSERT_GT(read(fd, buf, ARRAY_SIZE(buf)), 0);
> > +     VFIO_ASSERT_EQ(close(fd), 0);
> > +
> > +     return strtol(buf, NULL, 0);
> > +}
> > +
> > +static void sysfs_set_val(const char *component, const char *name,
> > +                       const char *file, const char *val)
> > +{
> > +     char path[PATH_MAX] = {0};
>
> Ditto here about zero-intialization being unnecessary.
>
> > +     int fd;
> > +
> > +     snprintf(path, PATH_MAX, "/sys/bus/pci/%s/%s/%s", component, name, file);
>
> Ditto here about snprintf_assert()
>
> You get the idea... I won't comment on the ones below.
>
> > +     VFIO_ASSERT_GT(fd = open(path, O_WRONLY), 0);
> > +
> > +     VFIO_ASSERT_EQ(write(fd, val, strlen(val)), strlen(val));
> > +     VFIO_ASSERT_EQ(close(fd), 0);
> > +}
> > +
> > +static int sysfs_get_device_val(const char *bdf, const char *file)
> > +{
> > +     sysfs_get_val("devices", bdf, file);
> > +}
> > +
> > +static void sysfs_set_device_val(const char *bdf, const char *file, const char *val)
> > +{
> > +     sysfs_set_val("devices", bdf, file, val);
> > +}
> > +
> > +static void sysfs_set_driver_val(const char *driver, const char *file, const char *val)
> > +{
> > +     sysfs_set_val("drivers", driver, file, val);
> > +}
> > +
> > +static void sysfs_set_device_val_int(const char *bdf, const char *file, int val)
> > +{
> > +     char val_str[32] = {0};
> > +
> > +     snprintf(val_str, sizeof(val_str), "%d", val);
> > +     sysfs_set_device_val(bdf, file, val_str);
> > +}
> > +
> > +int sysfs_get_sriov_totalvfs(const char *bdf)
> > +{
> > +     return sysfs_get_device_val(bdf, "sriov_totalvfs");
> > +}
> > +
> > +int sysfs_get_sriov_numvfs(const char *bdf)
> > +{
> > +     return sysfs_get_device_val(bdf, "sriov_numvfs");
> > +}
> > +
> > +void sysfs_set_sriov_numvfs(const char *bdf, int numvfs)
> > +{
> > +     sysfs_set_device_val_int(bdf, "sriov_numvfs", numvfs);
> > +}
> > +
> > +bool sysfs_get_sriov_drivers_autoprobe(const char *bdf)
> > +{
> > +     return (bool)sysfs_get_device_val(bdf, "sriov_drivers_autoprobe");
> > +}
> > +
> > +void sysfs_set_sriov_drivers_autoprobe(const char *bdf, bool val)
> > +{
> > +     sysfs_set_device_val_int(bdf, "sriov_drivers_autoprobe", val);
> > +}
> > +
> > +void sysfs_bind_driver(const char *bdf, const char *driver)
> > +{
> > +     sysfs_set_driver_val(driver, "bind", bdf);
> > +}
> > +
> > +void sysfs_unbind_driver(const char *bdf, const char *driver)
> > +{
> > +     sysfs_set_driver_val(driver, "unbind", bdf);
> > +}
> > +
> > +void sysfs_get_sriov_vf_bdf(const char *pf_bdf, int i, char *out_vf_bdf)
> > +{
> > +     char vf_path[PATH_MAX] = {0};
> > +     char path[PATH_MAX] = {0};
> > +     int ret;
> > +
> > +     snprintf(path, PATH_MAX, "/sys/bus/pci/devices/%s/virtfn%d", pf_bdf, i);
> > +
> > +     ret = readlink(path, vf_path, PATH_MAX);
> > +     VFIO_ASSERT_NE(ret, -1);
> > +
> > +     ret = sscanf(basename(vf_path), "%s", out_vf_bdf);
> > +     VFIO_ASSERT_EQ(ret, 1);
> > +}
> > +
> > +unsigned int sysfs_get_device_group(const char *bdf)
>
> nit: s/device_group/iommu_group/
>
> > +{
> > +     char dev_iommu_group_path[PATH_MAX] = {0};
> > +     char path[PATH_MAX] = {0};
> > +     unsigned int group;
> > +     int ret;
> > +
> > +     snprintf(path, PATH_MAX, "/sys/bus/pci/devices/%s/iommu_group", bdf);
> > +
> > +     ret = readlink(path, dev_iommu_group_path, sizeof(dev_iommu_group_path));
> > +     VFIO_ASSERT_NE(ret, -1, "Failed to get the IOMMU group for device: %s\n", bdf);
> > +
> > +     ret = sscanf(basename(dev_iommu_group_path), "%u", &group);
> > +     VFIO_ASSERT_EQ(ret, 1, "Failed to get the IOMMU group for device: %s\n", bdf);
> > +
> > +     return group;
> > +}
> > +
> > +int sysfs_get_driver(const char *bdf, char *out_driver)
> > +{
> > +     char driver_path[PATH_MAX] = {0};
> > +     char path[PATH_MAX] = {0};
> > +     int ret;
> > +
> > +     snprintf(path, PATH_MAX, "/sys/bus/pci/devices/%s/driver", bdf);
> > +     ret = readlink(path, driver_path, PATH_MAX);
> > +     if (ret == -1) {
> > +             if (errno == ENOENT)
> > +                     return -1;
> > +
> > +             VFIO_FAIL("Failed to read %s\n", path);
> > +     }
> > +
> > +     ret = sscanf(basename(driver_path), "%s", out_driver);
>
> I think this is equivalent to:
>
>   out_driver = basename(driver_path);
>
> ... which means out_driver to point within driver_path, which is stack
> allocated? I think you want to do strcpy() after basename() to copy the
> driver name to out_driver.
>
> Also how do you prevent overflowing out_driver? Maybe it would be
> cleaner for sysfs_get_driver() to allocate out_driver and return it to
> the caller?
>
> We can return an empty string for the ENOENT case.
>
Good point. Better to alloc 'out_driver'.

I'll take care of this and other nits that you pointed out in v3.

Thank you.
Raghavendra

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