Re: [RFC PATCH] net: devlink: devlink_nl_info_fill: populate default information

[Vincent MAILHOL]

On Wed. 23 nov. 2022 à 18:46, Jiri Pirko <jiri@xxxxxxxxxx> wrote:
> Tue, Nov 22, 2022 at 04:49:34PM CET, mailhol.vincent@xxxxxxxxxx wrote:
> >Some piece of information are common to the vast majority of the
> >devices. Examples are:
> >
> >  * the driver name.
> >  * the serial number of a USB device.
> >
> >Modify devlink_nl_info_fill() to retrieve those information so that
> >the drivers do not have to. Rationale: factorize code.
> >
> >Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> >---
> >I am sending this as an RFC because I just started to study devlink.
> >
> >I can see a parallel with ethtool for which the core will fill
> >whatever it can. c.f.:
> >commit f20a0a0519f3 ("ethtool: doc: clarify what drivers can implement in their get_drvinfo()")
> >Link: https://git.kernel.org/netdev/net-next/c/f20a0a0519f3
> >
> >I think that devlink should do the same.
> >
> >Right now, I identified two fields. If this RFC receive positive
> >feedback, I will iron it up and try to see if there is more that can
> >be filled by default.
> >
> >Thank you for your comments.
> >---
> > net/core/devlink.c | 36 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 36 insertions(+)
> >
> >diff --git a/net/core/devlink.c b/net/core/devlink.c
> >index 7f789bbcbbd7..1908b360caf7 100644
> >--- a/net/core/devlink.c
> >+++ b/net/core/devlink.c
> >@@ -18,6 +18,7 @@
> > #include <linux/netdevice.h>
> > #include <linux/spinlock.h>
> > #include <linux/refcount.h>
> >+#include <linux/usb.h>
> > #include <linux/workqueue.h>
> > #include <linux/u64_stats_sync.h>
> > #include <linux/timekeeping.h>
> >@@ -6685,12 +6686,37 @@ int devlink_info_version_running_put_ext(struct devlink_info_req *req,
> > }
> > EXPORT_SYMBOL_GPL(devlink_info_version_running_put_ext);
> >
> >+static int devlink_nl_driver_info_get(struct device_driver *drv,
> >+                                    struct devlink_info_req *req)
> >+{
> >+      if (!drv)
> >+              return 0;
> >+
> >+      if (drv->name[0])
> >+              return devlink_info_driver_name_put(req, drv->name);
>
> Make sure that this provides the same value for all existing drivers
> using devlink.

There are 21 drivers so far which reports the driver name through devlink. c.f.:
  $ git grep "devlink_info_driver_name_put(" drivers | wc -l

Out of those 21, there is only one: the mlxsw which seems to report
something different than device_driver::name. Instead it reports some
bus_info:
  https://elixir.bootlin.com/linux/v6.1-rc1/source/drivers/net/ethernet/mellanox/mlxsw/core.c#L1462
  https://elixir.bootlin.com/linux/v6.1-rc1/source/drivers/net/ethernet/mellanox/mlxsw/core.h#L504

I am not sure what the bus_info is here, but it looks like a misuse of
the field here.

>
> >+
> >+      return 0;
> >+}
> >+
> >+static int devlink_nl_usb_info_get(struct usb_device *udev,
> >+                                 struct devlink_info_req *req)
> >+{
> >+      if (!udev)
> >+              return 0;
> >+
> >+      if (udev->serial[0])
> >+              return devlink_info_serial_number_put(req, udev->serial);
> >+
> >+      return 0;
> >+}
> >+
> > static int
> > devlink_nl_info_fill(struct sk_buff *msg, struct devlink *devlink,
> >                    enum devlink_command cmd, u32 portid,
> >                    u32 seq, int flags, struct netlink_ext_ack *extack)
> > {
> >       struct devlink_info_req req = {};
> >+      struct device *dev = devlink_to_dev(devlink);
> >       void *hdr;
> >       int err;
> >
> >@@ -6707,6 +6733,16 @@ devlink_nl_info_fill(struct sk_buff *msg, struct devlink *devlink,
> >       if (err)
> >               goto err_cancel_msg;
> >
> >+      err = devlink_nl_driver_info_get(dev->driver, &req);
> >+      if (err)
> >+              goto err_cancel_msg;
> >+
> >+      if (!strcmp(dev->parent->type->name, "usb_device")) {
>
> Comparing to string does not seem correct here.

There is a is_usb_device() which does the check:
  https://elixir.bootlin.com/linux/v6.1-rc1/source/drivers/usb/core/usb.h#L152

but this macro is not exposed outside of the usb core. The string
comparison was the only solution I found.

Do you have any other ideas? If not and if this goes further than the
RFC stage, I will ask the USB folks if there is a better way.

>
> >+              err = devlink_nl_usb_info_get(to_usb_device(dev->parent), &req);
>
> As Jakub pointed out, you have to make sure that driver does not put the
> same attrs again. You have to introduce this functionality with removing
> the fill-ups in drivers atomically, in a single patch.

Either this, either track if the attribute is already set. I would
prefer to remove all drivers fill-ups but this is not feasible for the
serial number. c.f. my reply to Jacub in this thread:
  https://lore.kernel.org/netdev/CAMZ6RqJ8_=h1SS7WmBeEB=75wsvVUZrb-8ELCDtpZb0gSs=2+A@xxxxxxxxxxxxxx/

> >+              if (err)
> >+                      goto err_cancel_msg;
> >+      }
> >+
> >       genlmsg_end(msg, hdr);
> >       return 0;
> >
> >--
> >2.37.4
> >