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Message-ID: <aV7hDIe3tvehETXS@google.com>
Date: Wed, 7 Jan 2026 22:41:16 +0000
From: David Matlack <dmatlack@...gle.com>
To: Raghavendra Rao Ananta <rananta@...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 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.
> + VFIO_ASSERT_EQ(ret, 1);
> +
> + return 0;
> +}
> diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> index 64a19481b734f..9b2a123cee5fc 100644
> --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> @@ -22,8 +22,6 @@
> #include "../../../kselftest.h"
> #include <libvfio.h>
>
> -#define PCI_SYSFS_PATH "/sys/bus/pci/devices"
> -
> static void vfio_pci_irq_set(struct vfio_pci_device *device,
> u32 index, u32 vector, u32 count, int *fds)
> {
> @@ -181,24 +179,6 @@ void vfio_pci_device_reset(struct vfio_pci_device *device)
> ioctl_assert(device->fd, VFIO_DEVICE_RESET, NULL);
> }
>
> -static unsigned int vfio_pci_get_group_from_dev(const char *bdf)
> -{
> - char dev_iommu_group_path[PATH_MAX] = {0};
> - char sysfs_path[PATH_MAX] = {0};
> - unsigned int group;
> - int ret;
> -
> - snprintf_assert(sysfs_path, PATH_MAX, "%s/%s/iommu_group", PCI_SYSFS_PATH, bdf);
> -
> - ret = readlink(sysfs_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;
> -}
> -
> static void vfio_pci_group_setup(struct vfio_pci_device *device, const char *bdf)
> {
> struct vfio_group_status group_status = {
> @@ -207,7 +187,7 @@ static void vfio_pci_group_setup(struct vfio_pci_device *device, const char *bdf
> char group_path[32];
> int group;
>
> - group = vfio_pci_get_group_from_dev(bdf);
> + group = sysfs_get_device_group(bdf);
> snprintf_assert(group_path, sizeof(group_path), "/dev/vfio/%d", group);
>
> device->group_fd = open(group_path, O_RDWR);
> --
> 2.52.0.239.gd5f0c6e74e-goog
>
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