netdev - Re: [RFC PATCH net-next 2/4] switchdev: add fwd

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Message-ID: <CAE4R7bA_N0YtoNEWrX7kO=PA3nWNc-nGL0Bcyt_1SmeX9PZs_g@mail.gmail.com>
Date:	Sun, 14 Jun 2015 10:50:13 -0700
From:	Scott Feldman <sfeldma@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	Netdev <netdev@...r.kernel.org>,
	"simon.horman@...ronome.com" <simon.horman@...ronome.com>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	"Arad, Ronen" <ronen.arad@...el.com>,
	"Fastabend, John R" <john.r.fastabend@...el.com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	davidch <davidch@...adcom.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [RFC PATCH net-next 2/4] switchdev: add fwd_mark generator helper

On Sat, Jun 13, 2015 at 11:56 PM, Jiri Pirko <jiri@...nulli.us> wrote:
> Sat, Jun 13, 2015 at 08:04:28PM CEST, sfeldma@...il.com wrote:
>>From: Scott Feldman <sfeldma@...il.com>
>>
>>skb->fwd_mark and dev->fwd_mark are 32-bit and should be unique for device
>>and maybe even unique for a sub-set of ports within device, so add
>>switchdev helper function to generate unique marks based on driver-supplied
>>key.  Typically, the driver would use device switch ID for key, and maybe
>>additional fields in key for grouped ports such as bridge ifindex.  The key
>>can be of arbitrary length.
>>
>>The generator uses a global hash table to store fwd_marks hashed by key.
>>
>>Signed-off-by: Scott Feldman <sfeldma@...il.com>

<snip>

>>+u32 switchdev_mark_get(void *key, size_t key_len)
>>+{
>>+      struct switchdev_mark_ht_entry {
>>+              struct hlist_node entry;
>>+              void *key;
>>+              size_t key_len;
>>+              u32 key_crc32;
>>+              u32 mark;
>>+      } *entry;
>>+      u32 key_crc32 = crc32(~0, key, key_len);
>>+      u32 mark = 0;
>>+      unsigned long flags;
>>+
>>+      spin_lock_irqsave(&switchdev_mark_lock, flags);
>
> I fail to see why _irqsave variant is needed here.

I don't know what context caller is in, so using most conservative
spinlock.  Is there a better way?
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