Re: [PATCH 10/11] treewide: Manually convert custom kernel_param_ops .get callbacks

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, May 21, 2026 at 3:33 PM Kees Cook <kees@kernel.org> wrote:
>
> Convert struct kernel_param_ops .get callbacks from legacy "char *" to
> "struct seq_buf *".
>
> Since seq_buf_printf() will return -1 on overflow, and struct
> kernel_param_ops .get callbacks are expected to truncate without error,
> we must ignore the return value from seq_buf_print() and always return 0
> (as the length is calculated in the common dispatcher code).
>
> No struct kernel_param_ops initializations need changing since
> DEFINE_KERNEL_PARAM_OPS already routes the pointer to .get or .get_str
> via _Generic based on the function signature, so converted callbacks
> are automatically moved from the .get_str to the .get callback.
>
> Signed-off-by: Kees Cook <kees@kernel.org>

For ACPI:

Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>

> ---
>  include/linux/dynamic_debug.h            |  8 ++-
>  arch/um/drivers/vfio_kern.c              |  3 +-
>  arch/um/drivers/virtio_uml.c             | 12 ++--
>  drivers/acpi/button.c                    | 19 ++++--
>  drivers/acpi/sysfs.c                     | 83 +++++++++++-------------
>  drivers/char/ipmi/ipmi_watchdog.c        | 33 ++++------
>  drivers/firmware/qemu_fw_cfg.c           | 34 +++++-----
>  drivers/gpu/drm/i915/i915_mitigations.c  | 26 ++++----
>  drivers/infiniband/ulp/srp/ib_srp.c      |  7 +-
>  drivers/media/usb/uvc/uvc_driver.c       |  8 ++-
>  drivers/pci/pcie/aspm.c                  | 17 +++--
>  drivers/scsi/fcoe/fcoe_transport.c       | 22 +++----
>  drivers/thermal/intel/intel_powerclamp.c | 14 ++--
>  drivers/tty/hvc/hvc_iucv.c               | 18 ++---
>  drivers/usb/storage/usb.c                | 20 +++---
>  drivers/virtio/virtio_mmio.c             | 21 +++---
>  lib/dynamic_debug.c                      | 10 ++-
>  17 files changed, 178 insertions(+), 177 deletions(-)
>
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index 05743900a116..999a25671b6a 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -334,8 +334,10 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
>  extern int ddebug_dyndbg_module_param_cb(char *param, char *val,
>                                         const char *modname);
>  struct kernel_param;
> +struct seq_buf;
>  int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp);
> -int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp);
> +int param_get_dyndbg_classes(struct seq_buf *buffer,
> +                            const struct kernel_param *kp);
>
>  #else
>
> @@ -352,9 +354,11 @@ static inline int ddebug_dyndbg_module_param_cb(char *param, char *val,
>  }
>
>  struct kernel_param;
> +struct seq_buf;
>  static inline int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp)
>  { return 0; }
> -static inline int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
> +static inline int param_get_dyndbg_classes(struct seq_buf *buffer,
> +                                          const struct kernel_param *kp)
>  { return 0; }
>
>  #endif
> diff --git a/arch/um/drivers/vfio_kern.c b/arch/um/drivers/vfio_kern.c
> index fb7988dc5482..7c1119d0d9c1 100644
> --- a/arch/um/drivers/vfio_kern.c
> +++ b/arch/um/drivers/vfio_kern.c
> @@ -623,7 +623,8 @@ static int uml_vfio_cmdline_set(const char *device, const struct kernel_param *k
>         return 0;
>  }
>
> -static int uml_vfio_cmdline_get(char *buffer, const struct kernel_param *kp)
> +static int uml_vfio_cmdline_get(struct seq_buf *buffer,
> +                               const struct kernel_param *kp)
>  {
>         return 0;
>  }
> diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
> index f9ae745f4586..cea806540625 100644
> --- a/arch/um/drivers/virtio_uml.c
> +++ b/arch/um/drivers/virtio_uml.c
> @@ -1379,23 +1379,21 @@ static int vu_cmdline_get_device(struct device *dev, void *data)
>  {
>         struct platform_device *pdev = to_platform_device(dev);
>         struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
> -       char *buffer = data;
> -       unsigned int len = strlen(buffer);
> +       struct seq_buf *s = data;
>
> -       snprintf(buffer + len, PAGE_SIZE - len, "%s:%d:%d\n",
> -                pdata->socket_path, pdata->virtio_device_id, pdev->id);
> +       seq_buf_printf(s, "%s:%d:%d\n",
> +                      pdata->socket_path, pdata->virtio_device_id, pdev->id);
>         return 0;
>  }
>
> -static int vu_cmdline_get(char *buffer, const struct kernel_param *kp)
> +static int vu_cmdline_get(struct seq_buf *buffer, const struct kernel_param *kp)
>  {
>         guard(mutex)(&vu_cmdline_lock);
>
> -       buffer[0] = '\0';
>         if (vu_cmdline_parent_registered)
>                 device_for_each_child(&vu_cmdline_parent, buffer,
>                                       vu_cmdline_get_device);
> -       return strlen(buffer) + 1;
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(vu_cmdline_param_ops, vu_cmdline_set,
> diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
> index dc064a388c23..31c624bebc65 100644
> --- a/drivers/acpi/button.c
> +++ b/drivers/acpi/button.c
> @@ -715,19 +715,24 @@ static int param_set_lid_init_state(const char *val,
>         return 0;
>  }
>
> -static int param_get_lid_init_state(char *buf, const struct kernel_param *kp)
> +static int param_get_lid_init_state(struct seq_buf *buf,
> +                                   const struct kernel_param *kp)
>  {
> -       int i, c = 0;
> +       int i;
>
> -       for (i = 0; i < ARRAY_SIZE(lid_init_state_str); i++)
> +       for (i = 0; i < ARRAY_SIZE(lid_init_state_str); i++) {
>                 if (i == lid_init_state)
> -                       c += sprintf(buf + c, "[%s] ", lid_init_state_str[i]);
> +                       seq_buf_printf(buf, "[%s] ", lid_init_state_str[i]);
>                 else
> -                       c += sprintf(buf + c, "%s ", lid_init_state_str[i]);
> +                       seq_buf_printf(buf, "%s ", lid_init_state_str[i]);
> +       }
>
> -       buf[c - 1] = '\n'; /* Replace the final space with a newline */
> +       /* Replace the final space with a newline. */
> +       if (!seq_buf_has_overflowed(buf) && buf->len > 0 &&
> +           buf->buffer[buf->len - 1] == ' ')
> +               buf->buffer[buf->len - 1] = '\n';
>
> -       return c;
> +       return 0;
>  }
>
>  module_param_call(lid_init_state,
> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> index 5247ed7e05cc..dff7cc7da8bf 100644
> --- a/drivers/acpi/sysfs.c
> +++ b/drivers/acpi/sysfs.c
> @@ -89,53 +89,49 @@ static const struct acpi_dlevel acpi_debug_levels[] = {
>         ACPI_DEBUG_INIT(ACPI_LV_EVENTS),
>  };
>
> -static int param_get_debug_layer(char *buffer, const struct kernel_param *kp)
> +static int param_get_debug_layer(struct seq_buf *buffer,
> +                                const struct kernel_param *kp)
>  {
> -       int result = 0;
>         int i;
>
> -       result = sprintf(buffer, "%-25s\tHex        SET\n", "Description");
> +       seq_buf_printf(buffer, "%-25s\tHex        SET\n", "Description");
>
>         for (i = 0; i < ARRAY_SIZE(acpi_debug_layers); i++) {
> -               result += sprintf(buffer + result, "%-25s\t0x%08lX [%c]\n",
> -                                 acpi_debug_layers[i].name,
> -                                 acpi_debug_layers[i].value,
> -                                 (acpi_dbg_layer & acpi_debug_layers[i].value)
> -                                 ? '*' : ' ');
> +               seq_buf_printf(buffer, "%-25s\t0x%08lX [%c]\n",
> +                              acpi_debug_layers[i].name,
> +                              acpi_debug_layers[i].value,
> +                              (acpi_dbg_layer & acpi_debug_layers[i].value)
> +                              ? '*' : ' ');
>         }
> -       result +=
> -           sprintf(buffer + result, "%-25s\t0x%08X [%c]\n", "ACPI_ALL_DRIVERS",
> -                   ACPI_ALL_DRIVERS,
> -                   (acpi_dbg_layer & ACPI_ALL_DRIVERS) ==
> -                   ACPI_ALL_DRIVERS ? '*' : (acpi_dbg_layer & ACPI_ALL_DRIVERS)
> -                   == 0 ? ' ' : '-');
> -       result +=
> -           sprintf(buffer + result,
> -                   "--\ndebug_layer = 0x%08X ( * = enabled)\n",
> -                   acpi_dbg_layer);
> +       seq_buf_printf(buffer, "%-25s\t0x%08X [%c]\n", "ACPI_ALL_DRIVERS",
> +                      ACPI_ALL_DRIVERS,
> +                      (acpi_dbg_layer & ACPI_ALL_DRIVERS) == ACPI_ALL_DRIVERS
> +                      ? '*' : (acpi_dbg_layer & ACPI_ALL_DRIVERS) == 0
> +                      ? ' ' : '-');
> +       seq_buf_printf(buffer, "--\ndebug_layer = 0x%08X ( * = enabled)\n",
> +                      acpi_dbg_layer);
>
> -       return result;
> +       return 0;
>  }
>
> -static int param_get_debug_level(char *buffer, const struct kernel_param *kp)
> +static int param_get_debug_level(struct seq_buf *buffer,
> +                                const struct kernel_param *kp)
>  {
> -       int result = 0;
>         int i;
>
> -       result = sprintf(buffer, "%-25s\tHex        SET\n", "Description");
> +       seq_buf_printf(buffer, "%-25s\tHex        SET\n", "Description");
>
>         for (i = 0; i < ARRAY_SIZE(acpi_debug_levels); i++) {
> -               result += sprintf(buffer + result, "%-25s\t0x%08lX [%c]\n",
> -                                 acpi_debug_levels[i].name,
> -                                 acpi_debug_levels[i].value,
> -                                 (acpi_dbg_level & acpi_debug_levels[i].value)
> -                                 ? '*' : ' ');
> +               seq_buf_printf(buffer, "%-25s\t0x%08lX [%c]\n",
> +                              acpi_debug_levels[i].name,
> +                              acpi_debug_levels[i].value,
> +                              (acpi_dbg_level & acpi_debug_levels[i].value)
> +                              ? '*' : ' ');
>         }
> -       result +=
> -           sprintf(buffer + result, "--\ndebug_level = 0x%08X (* = enabled)\n",
> -                   acpi_dbg_level);
> +       seq_buf_printf(buffer, "--\ndebug_level = 0x%08X (* = enabled)\n",
> +                      acpi_dbg_level);
>
> -       return result;
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(param_ops_debug_layer, param_set_uint,
> @@ -247,16 +243,18 @@ static int param_set_trace_state(const char *val,
>         return 0;
>  }
>
> -static int param_get_trace_state(char *buffer, const struct kernel_param *kp)
> +static int param_get_trace_state(struct seq_buf *buffer,
> +                                const struct kernel_param *kp)
>  {
>         if (!(acpi_gbl_trace_flags & ACPI_TRACE_ENABLED))
> -               return sprintf(buffer, "disable\n");
> -       if (!acpi_gbl_trace_method_name)
> -               return sprintf(buffer, "enable\n");
> -       if (acpi_gbl_trace_flags & ACPI_TRACE_ONESHOT)
> -               return sprintf(buffer, "method-once\n");
> +               seq_buf_printf(buffer, "disable\n");
> +       else if (!acpi_gbl_trace_method_name)
> +               seq_buf_printf(buffer, "enable\n");
> +       else if (acpi_gbl_trace_flags & ACPI_TRACE_ONESHOT)
> +               seq_buf_printf(buffer, "method-once\n");
>         else
> -               return sprintf(buffer, "method\n");
> +               seq_buf_printf(buffer, "method\n");
> +       return 0;
>  }
>
>  module_param_call(trace_state, param_set_trace_state, param_get_trace_state,
> @@ -272,14 +270,11 @@ MODULE_PARM_DESC(aml_debug_output,
>                  "To enable/disable the ACPI Debug Object output.");
>
>  /* /sys/module/acpi/parameters/acpica_version */
> -static int param_get_acpica_version(char *buffer,
> +static int param_get_acpica_version(struct seq_buf *buffer,
>                                     const struct kernel_param *kp)
>  {
> -       int result;
> -
> -       result = sprintf(buffer, "%x\n", ACPI_CA_VERSION);
> -
> -       return result;
> +       seq_buf_printf(buffer, "%x\n", ACPI_CA_VERSION);
> +       return 0;
>  }
>
>  module_param_call(acpica_version, NULL, param_get_acpica_version, NULL, 0444);
> diff --git a/drivers/char/ipmi/ipmi_watchdog.c b/drivers/char/ipmi/ipmi_watchdog.c
> index 91a99417d204..2bfec85ef331 100644
> --- a/drivers/char/ipmi/ipmi_watchdog.c
> +++ b/drivers/char/ipmi/ipmi_watchdog.c
> @@ -197,11 +197,11 @@ static DEFINE_KERNEL_PARAM_OPS(param_ops_timeout, set_param_timeout,
>                                param_get_int);
>  #define param_check_timeout param_check_int
>
> -typedef int (*action_fn)(const char *intval, char *outval);
> +typedef int (*action_fn)(const char *intval, struct seq_buf *outval);
>
> -static int action_op(const char *inval, char *outval);
> -static int preaction_op(const char *inval, char *outval);
> -static int preop_op(const char *inval, char *outval);
> +static int action_op(const char *inval, struct seq_buf *outval);
> +static int preaction_op(const char *inval, struct seq_buf *outval);
> +static int preop_op(const char *inval, struct seq_buf *outval);
>  static void check_parms(void);
>
>  static int set_param_str(const char *val, const struct kernel_param *kp)
> @@ -227,20 +227,11 @@ static int set_param_str(const char *val, const struct kernel_param *kp)
>         return rv;
>  }
>
> -static int get_param_str(char *buffer, const struct kernel_param *kp)
> +static int get_param_str(struct seq_buf *buffer, const struct kernel_param *kp)
>  {
>         action_fn fn = (action_fn) kp->arg;
> -       int rv, len;
>
> -       rv = fn(NULL, buffer);
> -       if (rv)
> -               return rv;
> -
> -       len = strlen(buffer);
> -       buffer[len++] = '\n';
> -       buffer[len] = 0;
> -
> -       return len;
> +       return fn(NULL, buffer);
>  }
>
>
> @@ -1154,12 +1145,12 @@ static int action_op_set_val(const char *inval)
>         return 0;
>  }
>
> -static int action_op(const char *inval, char *outval)
> +static int action_op(const char *inval, struct seq_buf *outval)
>  {
>         int rv;
>
>         if (outval)
> -               strcpy(outval, action);
> +               seq_buf_printf(outval, "%s\n", action);
>
>         if (!inval)
>                 return 0;
> @@ -1186,12 +1177,12 @@ static int preaction_op_set_val(const char *inval)
>         return 0;
>  }
>
> -static int preaction_op(const char *inval, char *outval)
> +static int preaction_op(const char *inval, struct seq_buf *outval)
>  {
>         int rv;
>
>         if (outval)
> -               strcpy(outval, preaction);
> +               seq_buf_printf(outval, "%s\n", preaction);
>
>         if (!inval)
>                 return 0;
> @@ -1214,12 +1205,12 @@ static int preop_op_set_val(const char *inval)
>         return 0;
>  }
>
> -static int preop_op(const char *inval, char *outval)
> +static int preop_op(const char *inval, struct seq_buf *outval)
>  {
>         int rv;
>
>         if (outval)
> -               strcpy(outval, preop);
> +               seq_buf_printf(outval, "%s\n", preop);
>
>         if (!inval)
>                 return 0;
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index c87a5449ba8c..4ebc1e327849 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -860,7 +860,8 @@ static int fw_cfg_cmdline_set(const char *arg, const struct kernel_param *kp)
>         return PTR_ERR_OR_ZERO(fw_cfg_cmdline_dev);
>  }
>
> -static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
> +static int fw_cfg_cmdline_get(struct seq_buf *buf,
> +                             const struct kernel_param *kp)
>  {
>         /* stay silent if device was not configured via the command
>          * line, or if the parameter name (ioport/mmio) doesn't match
> @@ -873,22 +874,25 @@ static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
>
>         switch (fw_cfg_cmdline_dev->num_resources) {
>         case 1:
> -               return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_1_FMT,
> -                               resource_size(&fw_cfg_cmdline_dev->resource[0]),
> -                               fw_cfg_cmdline_dev->resource[0].start);
> +               seq_buf_printf(buf, PH_ADDR_PR_1_FMT,
> +                              resource_size(&fw_cfg_cmdline_dev->resource[0]),
> +                              fw_cfg_cmdline_dev->resource[0].start);
> +               return 0;
>         case 3:
> -               return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_3_FMT,
> -                               resource_size(&fw_cfg_cmdline_dev->resource[0]),
> -                               fw_cfg_cmdline_dev->resource[0].start,
> -                               fw_cfg_cmdline_dev->resource[1].start,
> -                               fw_cfg_cmdline_dev->resource[2].start);
> +               seq_buf_printf(buf, PH_ADDR_PR_3_FMT,
> +                              resource_size(&fw_cfg_cmdline_dev->resource[0]),
> +                              fw_cfg_cmdline_dev->resource[0].start,
> +                              fw_cfg_cmdline_dev->resource[1].start,
> +                              fw_cfg_cmdline_dev->resource[2].start);
> +               return 0;
>         case 4:
> -               return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_4_FMT,
> -                               resource_size(&fw_cfg_cmdline_dev->resource[0]),
> -                               fw_cfg_cmdline_dev->resource[0].start,
> -                               fw_cfg_cmdline_dev->resource[1].start,
> -                               fw_cfg_cmdline_dev->resource[2].start,
> -                               fw_cfg_cmdline_dev->resource[3].start);
> +               seq_buf_printf(buf, PH_ADDR_PR_4_FMT,
> +                              resource_size(&fw_cfg_cmdline_dev->resource[0]),
> +                              fw_cfg_cmdline_dev->resource[0].start,
> +                              fw_cfg_cmdline_dev->resource[1].start,
> +                              fw_cfg_cmdline_dev->resource[2].start,
> +                              fw_cfg_cmdline_dev->resource[3].start);
> +               return 0;
>         }
>
>         /* Should never get here */
> diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
> index 6061eae84e9c..99cb38f355b6 100644
> --- a/drivers/gpu/drm/i915/i915_mitigations.c
> +++ b/drivers/gpu/drm/i915/i915_mitigations.c
> @@ -95,33 +95,37 @@ static int mitigations_set(const char *val, const struct kernel_param *kp)
>         return 0;
>  }
>
> -static int mitigations_get(char *buffer, const struct kernel_param *kp)
> +static int mitigations_get(struct seq_buf *buffer,
> +                          const struct kernel_param *kp)
>  {
>         unsigned long local = READ_ONCE(mitigations);
> -       int count, i;
>         bool enable;
> +       int i;
>
> -       if (!local)
> -               return scnprintf(buffer, PAGE_SIZE, "%s\n", "off");
> +       if (!local) {
> +               seq_buf_printf(buffer, "%s\n", "off");
> +               return 0;
> +       }
>
>         if (local & BIT(BITS_PER_LONG - 1)) {
> -               count = scnprintf(buffer, PAGE_SIZE, "%s,", "auto");
> +               seq_buf_printf(buffer, "%s,", "auto");
>                 enable = false;
>         } else {
>                 enable = true;
> -               count = 0;
>         }
>
>         for (i = 0; i < ARRAY_SIZE(names); i++) {
>                 if ((local & BIT(i)) != enable)
>                         continue;
> -
> -               count += scnprintf(buffer + count, PAGE_SIZE - count,
> -                                  "%s%s,", enable ? "" : "!", names[i]);
> +               seq_buf_printf(buffer, "%s%s,", enable ? "" : "!", names[i]);
>         }
>
> -       buffer[count - 1] = '\n';
> -       return count;
> +       /* Replace the trailing comma with a newline. */
> +       if (!seq_buf_has_overflowed(buffer) && buffer->len > 0 &&
> +           buffer->buffer[buffer->len - 1] == ',')
> +               buffer->buffer[buffer->len - 1] = '\n';
> +
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(ops, mitigations_set, mitigations_get);
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index a81515f52a4f..4f53e939eec1 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -161,14 +161,15 @@ static struct ib_client srp_client = {
>
>  static struct ib_sa_client srp_sa_client;
>
> -static int srp_tmo_get(char *buffer, const struct kernel_param *kp)
> +static int srp_tmo_get(struct seq_buf *buffer, const struct kernel_param *kp)
>  {
>         int tmo = *(int *)kp->arg;
>
>         if (tmo >= 0)
> -               return sysfs_emit(buffer, "%d\n", tmo);
> +               seq_buf_printf(buffer, "%d\n", tmo);
>         else
> -               return sysfs_emit(buffer, "off\n");
> +               seq_buf_printf(buffer, "off\n");
> +       return 0;
>  }
>
>  static int srp_tmo_set(const char *val, const struct kernel_param *kp)
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 2338cab7fef9..1c5c40ce852d 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2451,12 +2451,14 @@ static int uvc_reset_resume(struct usb_interface *intf)
>   * Module parameters
>   */
>
> -static int uvc_clock_param_get(char *buffer, const struct kernel_param *kp)
> +static int uvc_clock_param_get(struct seq_buf *buffer,
> +                              const struct kernel_param *kp)
>  {
>         if (uvc_clock_param == CLOCK_MONOTONIC)
> -               return sprintf(buffer, "CLOCK_MONOTONIC");
> +               seq_buf_printf(buffer, "CLOCK_MONOTONIC");
>         else
> -               return sprintf(buffer, "CLOCK_REALTIME");
> +               seq_buf_printf(buffer, "CLOCK_REALTIME");
> +       return 0;
>  }
>
>  static int uvc_clock_param_set(const char *val, const struct kernel_param *kp)
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 925373b98dff..af2dd668fe4d 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1572,16 +1572,19 @@ static int pcie_aspm_set_policy(const char *val,
>         return 0;
>  }
>
> -static int pcie_aspm_get_policy(char *buffer, const struct kernel_param *kp)
> +static int pcie_aspm_get_policy(struct seq_buf *buffer,
> +                               const struct kernel_param *kp)
>  {
> -       int i, cnt = 0;
> -       for (i = 0; i < ARRAY_SIZE(policy_str); i++)
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(policy_str); i++) {
>                 if (i == aspm_policy)
> -                       cnt += sprintf(buffer + cnt, "[%s] ", policy_str[i]);
> +                       seq_buf_printf(buffer, "[%s] ", policy_str[i]);
>                 else
> -                       cnt += sprintf(buffer + cnt, "%s ", policy_str[i]);
> -       cnt += sprintf(buffer + cnt, "\n");
> -       return cnt;
> +                       seq_buf_printf(buffer, "%s ", policy_str[i]);
> +       }
> +       seq_buf_putc(buffer, '\n');
> +       return 0;
>  }
>
>  module_param_call(policy, pcie_aspm_set_policy, pcie_aspm_get_policy,
> diff --git a/drivers/scsi/fcoe/fcoe_transport.c b/drivers/scsi/fcoe/fcoe_transport.c
> index 88d85fc9a52a..aa10514ec46e 100644
> --- a/drivers/scsi/fcoe/fcoe_transport.c
> +++ b/drivers/scsi/fcoe/fcoe_transport.c
> @@ -23,7 +23,8 @@ MODULE_LICENSE("GPL v2");
>
>  static int fcoe_transport_create(const char *, const struct kernel_param *);
>  static int fcoe_transport_destroy(const char *, const struct kernel_param *);
> -static int fcoe_transport_show(char *buffer, const struct kernel_param *kp);
> +static int fcoe_transport_show(struct seq_buf *buffer,
> +                              const struct kernel_param *kp);
>  static struct fcoe_transport *fcoe_transport_lookup(struct net_device *device);
>  static struct fcoe_transport *fcoe_netdev_map_lookup(struct net_device *device);
>  static int fcoe_transport_enable(const char *, const struct kernel_param *);
> @@ -595,22 +596,21 @@ int fcoe_transport_detach(struct fcoe_transport *ft)
>  }
>  EXPORT_SYMBOL(fcoe_transport_detach);
>
> -static int fcoe_transport_show(char *buffer, const struct kernel_param *kp)
> +static int fcoe_transport_show(struct seq_buf *buffer,
> +                              const struct kernel_param *kp)
>  {
> -       int i, j;
>         struct fcoe_transport *ft = NULL;
>
> -       i = j = sprintf(buffer, "Attached FCoE transports:");
> +       seq_buf_printf(buffer, "Attached FCoE transports:");
>         mutex_lock(&ft_mutex);
> -       list_for_each_entry(ft, &fcoe_transports, list) {
> -               if (i >= PAGE_SIZE - IFNAMSIZ)
> -                       break;
> -               i += snprintf(&buffer[i], IFNAMSIZ, "%s ", ft->name);
> +       if (list_empty(&fcoe_transports)) {
> +               seq_buf_printf(buffer, "none");
> +       } else {
> +               list_for_each_entry(ft, &fcoe_transports, list)
> +                       seq_buf_printf(buffer, "%s ", ft->name);
>         }
>         mutex_unlock(&ft_mutex);
> -       if (i == j)
> -               i += snprintf(&buffer[i], IFNAMSIZ, "none");
> -       return i;
> +       return 0;
>  }
>
>  static int __init fcoe_transport_init(void)
> diff --git a/drivers/thermal/intel/intel_powerclamp.c b/drivers/thermal/intel/intel_powerclamp.c
> index 98fbc6892714..50ec1a0ff1ab 100644
> --- a/drivers/thermal/intel/intel_powerclamp.c
> +++ b/drivers/thermal/intel/intel_powerclamp.c
> @@ -101,15 +101,13 @@ static int duration_set(const char *arg, const struct kernel_param *kp)
>         return ret;
>  }
>
> -static int duration_get(char *buf, const struct kernel_param *kp)
> +static int duration_get(struct seq_buf *buf, const struct kernel_param *kp)
>  {
> -       int ret;
> -
>         mutex_lock(&powerclamp_lock);
> -       ret = sysfs_emit(buf, "%d\n", duration / 1000);
> +       seq_buf_printf(buf, "%d\n", duration / 1000);
>         mutex_unlock(&powerclamp_lock);
>
> -       return ret;
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(duration_ops, duration_set, duration_get);
> @@ -192,12 +190,14 @@ static int cpumask_set(const char *arg, const struct kernel_param *kp)
>         return ret;
>  }
>
> -static int cpumask_get(char *buf, const struct kernel_param *kp)
> +static int cpumask_get(struct seq_buf *buf, const struct kernel_param *kp)
>  {
>         if (!cpumask_available(idle_injection_cpu_mask))
>                 return -ENODEV;
>
> -       return cpumap_print_to_pagebuf(false, buf, idle_injection_cpu_mask);
> +       seq_buf_printf(buf, "%*pb\n", nr_cpu_ids,
> +                      cpumask_bits(idle_injection_cpu_mask));
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(cpumask_ops, cpumask_set, cpumask_get);
> diff --git a/drivers/tty/hvc/hvc_iucv.c b/drivers/tty/hvc/hvc_iucv.c
> index 29612a4a32cb..b27c1dfbd249 100644
> --- a/drivers/tty/hvc/hvc_iucv.c
> +++ b/drivers/tty/hvc/hvc_iucv.c
> @@ -1256,36 +1256,32 @@ static int param_set_vmidfilter(const char *val, const struct kernel_param *kp)
>
>  /**
>   * param_get_vmidfilter() - Get z/VM user ID filter
> - * @buffer:    Buffer to store z/VM user ID filter,
> - *             (buffer size assumption PAGE_SIZE)
> + * @buffer:    seq_buf to store z/VM user ID filter
>   * @kp:                Kernel parameter pointing to the hvc_iucv_filter array
>   *
>   * The function stores the filter as a comma-separated list of z/VM user IDs
>   * in @buffer. Typically, sysfs routines call this function for attr show.
>   */
> -static int param_get_vmidfilter(char *buffer, const struct kernel_param *kp)
> +static int param_get_vmidfilter(struct seq_buf *buffer,
> +                               const struct kernel_param *kp)
>  {
> -       int rc;
>         size_t index, len;
>         void *start, *end;
>
>         if (!machine_is_vm() || !hvc_iucv_devices)
>                 return -ENODEV;
>
> -       rc = 0;
>         read_lock_bh(&hvc_iucv_filter_lock);
>         for (index = 0; index < hvc_iucv_filter_size; index++) {
>                 start = hvc_iucv_filter + (8 * index);
>                 end   = memchr(start, ' ', 8);
>                 len   = (end) ? end - start : 8;
> -               memcpy(buffer + rc, start, len);
> -               rc += len;
> -               buffer[rc++] = ',';
> +               if (index)
> +                       seq_buf_putc(buffer, ',');
> +               seq_buf_printf(buffer, "%.*s", (int)len, (char *)start);
>         }
>         read_unlock_bh(&hvc_iucv_filter_lock);
> -       if (rc)
> -               buffer[--rc] = '\0';    /* replace last comma and update rc */
> -       return rc;
> +       return 0;
>  }
>
>  #define param_check_vmidfilter(name, p) __param_check(name, p, void)
> diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
> index 71dd623b95c9..637e1b8f622f 100644
> --- a/drivers/usb/storage/usb.c
> +++ b/drivers/usb/storage/usb.c
> @@ -115,27 +115,22 @@ static int parse_delay_str(const char *str, int ndecimals, const char *suffix,
>   * @val: The integer value to format, scaled by 10^(@ndecimals).
>   * @ndecimals: Number of decimal to scale down.
>   * @suffix: Suffix string to format.
> - * @str: Where to store the formatted string.
> - * @size: The size of buffer for @str.
> + * @s: Where to store the formatted string.
>   *
>   * Format an integer value in @val scale down by 10^(@ndecimals) without @suffix
>   * if @val is divisible by 10^(@ndecimals).
>   * Otherwise format a value in @val just as it is with @suffix
> - *
> - * Returns the number of characters written into @str.
>   */
> -static int format_delay_ms(unsigned int val, int ndecimals, const char *suffix,
> -                       char *str, int size)
> +static void format_delay_ms(unsigned int val, int ndecimals, const char *suffix,
> +                           struct seq_buf *s)
>  {
>         u64 delay_ms = val;
>         unsigned int rem = do_div(delay_ms, int_pow(10, ndecimals));
> -       int ret;
>
>         if (rem)
> -               ret = scnprintf(str, size, "%u%s\n", val, suffix);
> +               seq_buf_printf(s, "%u%s\n", val, suffix);
>         else
> -               ret = scnprintf(str, size, "%u\n", (unsigned int)delay_ms);
> -       return ret;
> +               seq_buf_printf(s, "%u\n", (unsigned int)delay_ms);
>  }
>
>  static int delay_use_set(const char *s, const struct kernel_param *kp)
> @@ -151,11 +146,12 @@ static int delay_use_set(const char *s, const struct kernel_param *kp)
>         return 0;
>  }
>
> -static int delay_use_get(char *s, const struct kernel_param *kp)
> +static int delay_use_get(struct seq_buf *s, const struct kernel_param *kp)
>  {
>         unsigned int delay_ms = *((unsigned int *)kp->arg);
>
> -       return format_delay_ms(delay_ms, 3, "ms", s, PAGE_SIZE);
> +       format_delay_ms(delay_ms, 3, "ms", s);
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(delay_use_ops, delay_use_set, delay_use_get);
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index f6df9c76ee81..81a7455e4643 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -728,24 +728,21 @@ static int vm_cmdline_set(const char *device,
>
>  static int vm_cmdline_get_device(struct device *dev, void *data)
>  {
> -       char *buffer = data;
> -       unsigned int len = strlen(buffer);
> +       struct seq_buf *s = data;
>         struct platform_device *pdev = to_platform_device(dev);
>
> -       snprintf(buffer + len, PAGE_SIZE - len, "0x%llx@0x%llx:%llu:%d\n",
> -                       pdev->resource[0].end - pdev->resource[0].start + 1ULL,
> -                       (unsigned long long)pdev->resource[0].start,
> -                       (unsigned long long)pdev->resource[1].start,
> -                       pdev->id);
> +       seq_buf_printf(s, "0x%llx@0x%llx:%llu:%d\n",
> +                      pdev->resource[0].end - pdev->resource[0].start + 1ULL,
> +                      (unsigned long long)pdev->resource[0].start,
> +                      (unsigned long long)pdev->resource[1].start,
> +                      pdev->id);
>         return 0;
>  }
>
> -static int vm_cmdline_get(char *buffer, const struct kernel_param *kp)
> +static int vm_cmdline_get(struct seq_buf *s, const struct kernel_param *kp)
>  {
> -       buffer[0] = '\0';
> -       device_for_each_child(&vm_cmdline_parent, buffer,
> -                       vm_cmdline_get_device);
> -       return strlen(buffer) + 1;
> +       device_for_each_child(&vm_cmdline_parent, s, vm_cmdline_get_device);
> +       return 0;
>  }
>
>  static DEFINE_KERNEL_PARAM_OPS(vm_cmdline_param_ops, vm_cmdline_set,
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index cf0405ba0dbd..123f061c2fb2 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -17,6 +17,7 @@
>  #include <linux/module.h>
>  #include <linux/moduleparam.h>
>  #include <linux/kallsyms.h>
> +#include <linux/seq_buf.h>
>  #include <linux/types.h>
>  #include <linux/mutex.h>
>  #include <linux/proc_fs.h>
> @@ -787,7 +788,8 @@ EXPORT_SYMBOL(param_set_dyndbg_classes);
>   * altered by direct >control.  Displays 0x for DISJOINT, 0-N for
>   * LEVEL Returns: #chars written or <0 on error
>   */
> -int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
> +int param_get_dyndbg_classes(struct seq_buf *buffer,
> +                            const struct kernel_param *kp)
>  {
>         const struct ddebug_class_param *dcp = kp->arg;
>         const struct ddebug_class_map *map = dcp->map;
> @@ -796,11 +798,13 @@ int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
>
>         case DD_CLASS_TYPE_DISJOINT_NAMES:
>         case DD_CLASS_TYPE_DISJOINT_BITS:
> -               return scnprintf(buffer, PAGE_SIZE, "0x%lx\n", *dcp->bits);
> +               seq_buf_printf(buffer, "0x%lx\n", *dcp->bits);
> +               return 0;
>
>         case DD_CLASS_TYPE_LEVEL_NAMES:
>         case DD_CLASS_TYPE_LEVEL_NUM:
> -               return scnprintf(buffer, PAGE_SIZE, "%d\n", *dcp->lvl);
> +               seq_buf_printf(buffer, "%d\n", *dcp->lvl);
> +               return 0;
>         default:
>                 return -1;
>         }
> --
> 2.34.1
>