Introduce a sysfs library to handle the common reads/writes to the
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.
Since readlink() is quite commonly used in the lib, introduce and use
readlink_safe() to take care of potential buffer overrun errors and to
safely terminate the buffer with '\0'.
Opportunistically, move vfio_pci_get_group_from_dev() to this library as
it falls under the same bucket. Rename it to sysfs_iommu_group_get() to
align with other function names.
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
---
.../selftests/vfio/lib/include/libvfio.h | 1 +
.../vfio/lib/include/libvfio/sysfs.h | 12 ++
tools/testing/selftests/vfio/lib/libvfio.mk | 1 +
tools/testing/selftests/vfio/lib/sysfs.c | 150 ++++++++++++++++++
.../selftests/vfio/lib/vfio_pci_device.c | 22 +--
5 files changed, 165 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 1b6da54cc2cb7..07862b470777b 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..c1d945ea62a10
--- /dev/null
+++ b/tools/testing/selftests/vfio/lib/include/libvfio/sysfs.h
@@ -0,0 +1,12 @@
+/* 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_sriov_totalvfs_get(const char *bdf);
+int sysfs_sriov_numvfs_get(const char *bdf);
+void sysfs_sriov_numvfs_set(const char *bdfs, int numvfs);
+char *sysfs_sriov_vf_bdf_get(const char *pf_bdf, int i);
+int sysfs_iommu_group_get(const char *bdf);
+char *sysfs_driver_get(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..f1e6889556527
--- /dev/null
+++ b/tools/testing/selftests/vfio/lib/sysfs.c
@@ -0,0 +1,150 @@
+// 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>
+
+/* Enough to hold MODULE_NAME_LEN */
+#define DRIVER_NAME_SZ 64
+
+#define readlink_safe(_path, _buf) ({ \
+ int __ret = readlink(_path, _buf, sizeof(_buf) - 1); \
+ if (__ret != -1) \
+ _buf[__ret] = 0; \
+ __ret; \
+})
+
+static void readlink_base(const char *path, const char *data_fmt, void *out_data)
+{
+ char rl_path[PATH_MAX];
+ int ret;
+
+ ret = readlink_safe(path, rl_path);
+ VFIO_ASSERT_NE(ret, -1);
+
+ ret = sscanf(basename(rl_path), data_fmt, out_data);
+ VFIO_ASSERT_EQ(ret, 1);
+}
+
+static int sysfs_val_get_int(const char *component, const char *name,
+ const char *file)
+{
+ char path[PATH_MAX];
+ char buf[32];
+ int ret;
+ int fd;
+
+ snprintf_assert(path, PATH_MAX, "/sys/bus/pci/%s/%s/%s", component, name, file);
+ 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);
+
+ errno = 0;
+ ret = strtol(buf, NULL, 0);
+ VFIO_ASSERT_EQ(errno, 0, "sysfs path \"%s\" is not an integer: \"%s\"\n", path, buf);
+
+ return ret;
+}
+
+static void sysfs_val_set(const char *component, const char *name,
+ const char *file, const char *val)
+{
+ char path[PATH_MAX];
+ int fd;
+
+ snprintf_assert(path, PATH_MAX, "/sys/bus/pci/%s/%s/%s", component, name, file);
+ 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_device_val_get(const char *bdf, const char *file)
+{
+ return sysfs_val_get_int("devices", bdf, file);
+}
+
+static void sysfs_device_val_set(const char *bdf, const char *file, const char *val)
+{
+ sysfs_val_set("devices", bdf, file, val);
+}
+
+static void sysfs_device_val_set_int(const char *bdf, const char *file, int val)
+{
+ char val_str[32];
+
+ snprintf_assert(val_str, sizeof(val_str), "%d", val);
+ sysfs_device_val_set(bdf, file, val_str);
+}
+
+int sysfs_sriov_totalvfs_get(const char *bdf)
+{
+ return sysfs_device_val_get(bdf, "sriov_totalvfs");
+}
+
+int sysfs_sriov_numvfs_get(const char *bdf)
+{
+ return sysfs_device_val_get(bdf, "sriov_numvfs");
+}
+
+void sysfs_sriov_numvfs_set(const char *bdf, int numvfs)
+{
+ sysfs_device_val_set_int(bdf, "sriov_numvfs", numvfs);
+}
+
+char *sysfs_sriov_vf_bdf_get(const char *pf_bdf, int i)
+{
+ char path[PATH_MAX];
+ char *out_vf_bdf;
+
+ /* Fit "0000:00:00.0" */
+ out_vf_bdf = calloc(16, sizeof(char));
+ VFIO_ASSERT_NOT_NULL(out_vf_bdf);
+
+ snprintf_assert(path, PATH_MAX, "/sys/bus/pci/devices/%s/virtfn%d", pf_bdf, i);
+ readlink_base(path, "%s", out_vf_bdf);
+
+ return out_vf_bdf;
+}
+
+int sysfs_iommu_group_get(const char *bdf)
+{
+ char path[PATH_MAX];
+ int group;
+
+ snprintf_assert(path, PATH_MAX, "/sys/bus/pci/devices/%s/iommu_group", bdf);
+ readlink_base(path, "%d", &group);
+
+ return group;
+}
+
+char *sysfs_driver_get(const char *bdf)
+{
+ char driver_path[PATH_MAX];
+ char path[PATH_MAX];
+ char *out_driver;
+ int ret;
+
+ out_driver = calloc(DRIVER_NAME_SZ, sizeof(char));
+ VFIO_ASSERT_NOT_NULL(out_driver);
+
+ snprintf_assert(path, PATH_MAX, "/sys/bus/pci/devices/%s/driver", bdf);
+ ret = readlink_safe(path, driver_path);
+ if (ret == -1) {
+ free(out_driver);
+
+ if (errno == ENOENT)
+ return NULL;
+
+ VFIO_FAIL("Failed to read %s\n", path);
+ }
+
+ strncpy(out_driver, basename(driver_path), DRIVER_NAME_SZ - 1);
+ return out_driver;
+}
diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index 1538d2b30ae59..82f255f0486dc 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -25,8 +25,6 @@
#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)
{
@@ -202,24 +200,6 @@ 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 = {
@@ -228,7 +208,7 @@ 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_iommu_group_get(bdf);
snprintf_assert(group_path, sizeof(group_path), "/dev/vfio/%d", group);
device->group_fd = open(group_path, O_RDWR);
--
2.53.0.1213.gd9a14994de-googOn Thu, 2 Apr 2026 17:30:54 +0000
Raghavendra Rao Ananta <rananta@google.com> wrote:
> diff --git a/tools/testing/selftests/vfio/lib/sysfs.c b/tools/testing/selftests/vfio/lib/sysfs.c
> new file mode 100644
> index 0000000000000..f1e6889556527
> --- /dev/null
> +++ b/tools/testing/selftests/vfio/lib/sysfs.c
> @@ -0,0 +1,150 @@
> +// 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>
> +
> +/* Enough to hold MODULE_NAME_LEN */
> +#define DRIVER_NAME_SZ 64
> +
> +#define readlink_safe(_path, _buf) ({ \
> + int __ret = readlink(_path, _buf, sizeof(_buf) - 1); \
> + if (__ret != -1) \
> + _buf[__ret] = 0; \
> + __ret; \
> +})
Not a current issue, but the use of sizeof() here is a danger for
future users that might pass something other than a stack array. We
could avoid this by adding a build time test (untested):
_Static_assert(!__builtin_types_compatible_p( \
__typeof__(_buf), char *), \
"readlink_safe: _buf must be an array, not a pointer"); \
Maybe overkill for an internal helper, but we could avoid the hazard.
...
> +char *sysfs_driver_get(const char *bdf)
> +{
> + char driver_path[PATH_MAX];
> + char path[PATH_MAX];
> + char *out_driver;
> + int ret;
> +
> + out_driver = calloc(DRIVER_NAME_SZ, sizeof(char));
> + VFIO_ASSERT_NOT_NULL(out_driver);
> +
> + snprintf_assert(path, PATH_MAX, "/sys/bus/pci/devices/%s/driver", bdf);
> + ret = readlink_safe(path, driver_path);
> + if (ret == -1) {
> + free(out_driver);
> +
> + if (errno == ENOENT)
> + return NULL;
> +
> + VFIO_FAIL("Failed to read %s\n", path);
> + }
> +
> + strncpy(out_driver, basename(driver_path), DRIVER_NAME_SZ - 1);
Nit, I'm not really sure what DRIVER_NAME_SZ buys us other than an
artificial limit. We're already bound by PATH_MAX and could just do a
strdup() for the return. Neither are blockers. Thanks,
Alex
> + return out_driver;
> +}
On Mon, Apr 6, 2026 at 2:12 PM Alex Williamson <alex@shazbot.org> wrote:
>
> On Thu, 2 Apr 2026 17:30:54 +0000
> Raghavendra Rao Ananta <rananta@google.com> wrote:
> > diff --git a/tools/testing/selftests/vfio/lib/sysfs.c b/tools/testing/selftests/vfio/lib/sysfs.c
> > new file mode 100644
> > index 0000000000000..f1e6889556527
> > --- /dev/null
> > +++ b/tools/testing/selftests/vfio/lib/sysfs.c
> > @@ -0,0 +1,150 @@
> > +// 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>
> > +
> > +/* Enough to hold MODULE_NAME_LEN */
> > +#define DRIVER_NAME_SZ 64
> > +
> > +#define readlink_safe(_path, _buf) ({ \
> > + int __ret = readlink(_path, _buf, sizeof(_buf) - 1); \
> > + if (__ret != -1) \
> > + _buf[__ret] = 0; \
> > + __ret; \
> > +})
>
> Not a current issue, but the use of sizeof() here is a danger for
> future users that might pass something other than a stack array. We
> could avoid this by adding a build time test (untested):
>
> _Static_assert(!__builtin_types_compatible_p( \
> __typeof__(_buf), char *), \
> "readlink_safe: _buf must be an array, not a pointer"); \
>
> Maybe overkill for an internal helper, but we could avoid the hazard.
>
Good point! It makes sense to have a build-time check for this. I will
incorporate the _Static_assert to avoid the hazard.
> ...
> > +char *sysfs_driver_get(const char *bdf)
> > +{
> > + char driver_path[PATH_MAX];
> > + char path[PATH_MAX];
> > + char *out_driver;
> > + int ret;
> > +
> > + out_driver = calloc(DRIVER_NAME_SZ, sizeof(char));
> > + VFIO_ASSERT_NOT_NULL(out_driver);
> > +
> > + snprintf_assert(path, PATH_MAX, "/sys/bus/pci/devices/%s/driver", bdf);
> > + ret = readlink_safe(path, driver_path);
> > + if (ret == -1) {
> > + free(out_driver);
> > +
> > + if (errno == ENOENT)
> > + return NULL;
> > +
> > + VFIO_FAIL("Failed to read %s\n", path);
> > + }
> > +
> > + strncpy(out_driver, basename(driver_path), DRIVER_NAME_SZ - 1);
>
> Nit, I'm not really sure what DRIVER_NAME_SZ buys us other than an
> artificial limit. We're already bound by PATH_MAX and could just do a
> strdup() for the return. Neither are blockers. Thanks,
>
Ah, why didn't I think of strdup(). It's a better approach. I'll
update this in v8.
Thank you.
Raghavendra
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