> -----Original Message-----
> From: netdev-ow...@vger.kernel.org <netdev-ow...@vger.kernel.org> On
> Behalf Of Jakub Kicinski
> Sent: Wednesday, April 29, 2020 4:38 PM
> To: da...@davemloft.net; j...@resnulli.us
> Cc: netdev@vger.kernel.org; kernel-t...@fb.com; Keller, Jacob E
> <jacob.e.kel...@intel.com>; Jakub Kicinski <k...@kernel.org>
> Subject: [PATCH net-next v2] devlink: let kernel allocate region snapshot id
> 
> Currently users have to choose a free snapshot id before
> calling DEVLINK_CMD_REGION_NEW. This is potentially racy
> and inconvenient.
> 
> Make the DEVLINK_ATTR_REGION_SNAPSHOT_ID optional and try
> to allocate id automatically. Send a message back to the
> caller with the snapshot info.
> 
> The message carrying id gets sent immediately, but the
> allocation is only valid if the entire operation succeeded.
> This makes life easier, as sending the notification itself
> may fail.

I like this. Not having to plan ahead and pick a random id is pretty useful, 
and this helps avoid some of the race that could occur around this.

Reviewed-by: Jacob Keller <jacob.e.kel...@intel.com>

Thanks,
Jake

> 
> Example use:
> $ devlink region new netdevsim/netdevsim1/dummy
> netdevsim/netdevsim1/dummy: snapshot 1
> 
> $ id=$(devlink -j region new netdevsim/netdevsim1/dummy | \
>        jq '.[][][][]')
> $ devlink region dump netdevsim/netdevsim1/dummy snapshot $id
> [...]
> $ devlink region del netdevsim/netdevsim1/dummy snapshot $id
> 
> v2:
>  - don't wrap the line containing extack;
>  - add a few sentences to the docs.
> 
> Signed-off-by: Jakub Kicinski <k...@kernel.org>
> ---
>  .../networking/devlink/devlink-region.rst     | 10 ++-
>  net/core/devlink.c                            | 83 ++++++++++++++++---
>  .../drivers/net/netdevsim/devlink.sh          | 13 +++
>  3 files changed, 91 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/networking/devlink/devlink-region.rst
> b/Documentation/networking/devlink/devlink-region.rst
> index 04e04d1ff627..b163d09a3d0d 100644
> --- a/Documentation/networking/devlink/devlink-region.rst
> +++ b/Documentation/networking/devlink/devlink-region.rst
> @@ -23,7 +23,12 @@ states, but see also :doc:`devlink-health`
>  Regions may optionally support capturing a snapshot on demand via the
>  ``DEVLINK_CMD_REGION_NEW`` netlink message. A driver wishing to allow
>  requested snapshots must implement the ``.snapshot`` callback for the region
> -in its ``devlink_region_ops`` structure.
> +in its ``devlink_region_ops`` structure. If snapshot id is not set in
> +the ``DEVLINK_CMD_REGION_NEW`` request kernel will allocate one and send
> +the snapshot information to user space. Note that receiving the snapshot
> +information does not guarantee that the snapshot creation completed
> +successfully, user space must check the status of the operation before
> +proceeding.
> 
>  example usage
>  -------------
> @@ -45,7 +50,8 @@ example usage
>      $ devlink region del pci/0000:00:05.0/cr-space snapshot 1
> 
>      # Request an immediate snapshot, if supported by the region
> -    $ devlink region new pci/0000:00:05.0/cr-space snapshot 5
> +    $ devlink region new pci/0000:00:05.0/cr-space
> +    pci/0000:00:05.0/cr-space: snapshot 5
> 
>      # Dump a snapshot:
>      $ devlink region dump pci/0000:00:05.0/fw-health snapshot 1
> diff --git a/net/core/devlink.c b/net/core/devlink.c
> index 1ec2e9fd8898..82703be1032e 100644
> --- a/net/core/devlink.c
> +++ b/net/core/devlink.c
> @@ -4065,10 +4065,64 @@ static int devlink_nl_cmd_region_del(struct sk_buff
> *skb,
>       return 0;
>  }
> 
> +static int
> +devlink_nl_alloc_snapshot_id(struct devlink *devlink, struct genl_info *info,
> +                          struct devlink_region *region, u32 *snapshot_id)
> +{
> +     struct sk_buff *msg;
> +     void *hdr;
> +     int err;
> +
> +     err = __devlink_region_snapshot_id_get(devlink, snapshot_id);
> +     if (err) {
> +             NL_SET_ERR_MSG_MOD(info->extack, "Failed to allocate a new
> snapshot id");
> +             return err;
> +     }
> +
> +     msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> +     if (!msg) {
> +             err = -ENOMEM;
> +             goto err_msg_alloc;
> +     }
> +
> +     hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq,
> +                       &devlink_nl_family, 0, DEVLINK_CMD_REGION_NEW);
> +     if (!hdr) {
> +             err = -EMSGSIZE;
> +             goto err_put_failure;
> +     }
> +     err = devlink_nl_put_handle(msg, devlink);
> +     if (err)
> +             goto err_attr_failure;
> +     err = nla_put_string(msg, DEVLINK_ATTR_REGION_NAME, region->ops-
> >name);
> +     if (err)
> +             goto err_attr_failure;
> +     err = nla_put_u32(msg, DEVLINK_ATTR_REGION_SNAPSHOT_ID,
> *snapshot_id);
> +     if (err)
> +             goto err_attr_failure;
> +     genlmsg_end(msg, hdr);
> +
> +     err = genlmsg_reply(msg, info);
> +     if (err)
> +             goto err_reply;
> +
> +     return 0;
> +
> +err_attr_failure:
> +     genlmsg_cancel(msg, hdr);
> +err_put_failure:
> +     nlmsg_free(msg);
> +err_msg_alloc:
> +err_reply:
> +     __devlink_snapshot_id_decrement(devlink, *snapshot_id);
> +     return err;
> +}
> +
>  static int
>  devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
>  {
>       struct devlink *devlink = info->user_ptr[0];
> +     struct nlattr *snapshot_id_attr;
>       struct devlink_region *region;
>       const char *region_name;
>       u32 snapshot_id;
> @@ -4080,11 +4134,6 @@ devlink_nl_cmd_region_new(struct sk_buff *skb,
> struct genl_info *info)
>               return -EINVAL;
>       }
> 
> -     if (!info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]) {
> -             NL_SET_ERR_MSG_MOD(info->extack, "No snapshot id
> provided");
> -             return -EINVAL;
> -     }
> -
>       region_name = nla_data(info->attrs[DEVLINK_ATTR_REGION_NAME]);
>       region = devlink_region_get_by_name(devlink, region_name);
>       if (!region) {
> @@ -4102,16 +4151,24 @@ devlink_nl_cmd_region_new(struct sk_buff *skb,
> struct genl_info *info)
>               return -ENOSPC;
>       }
> 
> -     snapshot_id = nla_get_u32(info-
> >attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]);
> +     snapshot_id_attr = info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID];
> +     if (snapshot_id_attr) {
> +             snapshot_id = nla_get_u32(snapshot_id_attr);
> 
> -     if (devlink_region_snapshot_get_by_id(region, snapshot_id)) {
> -             NL_SET_ERR_MSG_MOD(info->extack, "The requested snapshot
> id is already in use");
> -             return -EEXIST;
> -     }
> +             if (devlink_region_snapshot_get_by_id(region, snapshot_id)) {
> +                     NL_SET_ERR_MSG_MOD(info->extack, "The requested
> snapshot id is already in use");
> +                     return -EEXIST;
> +             }
> 
> -     err = __devlink_snapshot_id_insert(devlink, snapshot_id);
> -     if (err)
> -             return err;
> +             err = __devlink_snapshot_id_insert(devlink, snapshot_id);
> +             if (err)
> +                     return err;
> +     } else {
> +             err = devlink_nl_alloc_snapshot_id(devlink, info,
> +                                                region, &snapshot_id);
> +             if (err)
> +                     return err;
> +     }
> 
>       err = region->ops->snapshot(devlink, info->extack, &data);
>       if (err)
> diff --git a/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
> b/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
> index 9f9741444549..ad539eccddcb 100755
> --- a/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
> +++ b/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
> @@ -151,6 +151,19 @@ regions_test()
> 
>       check_region_snapshot_count dummy post-second-delete 2
> 
> +     sid=$(devlink -j region new $DL_HANDLE/dummy | jq '.[][][][]')
> +     check_err $? "Failed to create a new snapshot with id allocated by the
> kernel"
> +
> +     check_region_snapshot_count dummy post-first-request 3
> +
> +     devlink region dump $DL_HANDLE/dummy snapshot $sid >> /dev/null
> +     check_err $? "Failed to dump a snapshot with id allocated by the kernel"
> +
> +     devlink region del $DL_HANDLE/dummy snapshot $sid
> +     check_err $? "Failed to delete snapshot with id allocated by the kernel"
> +
> +     check_region_snapshot_count dummy post-first-request 2
> +
>       log_test "regions test"
>  }
> 
> --
> 2.25.4

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