* [PATCH] net: fix comment above build_skb()
@ 2013-07-23 15:39 Florian Fainelli
2013-07-23 15:49 ` Eric Dumazet
0 siblings, 1 reply; 5+ messages in thread
From: Florian Fainelli @ 2013-07-23 15:39 UTC (permalink / raw)
To: davem; +Cc: eric.dumazet, netdev, Florian Fainelli
build_skb() specifies that the data parameter must come from a kmalloc'd
area, this is only true if frag_size equals 0, because then build_skb()
will use kzsize(data) to figure out the actual data size. Update the
comment to reflect that special condition.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
net/core/skbuff.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 20e02d2..d3174db 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -309,7 +309,8 @@ EXPORT_SYMBOL(__alloc_skb);
* @frag_size: size of fragment, or 0 if head was kmalloced
*
* Allocate a new &sk_buff. Caller provides space holding head and
- * skb_shared_info. @data must have been allocated by kmalloc()
+ * skb_shared_info. @data must have been allocated by kmalloc() only if
+ * @frag_size is 0.
* The return is the new skb buffer.
* On a failure the return is %NULL, and @data is not freed.
* Notes :
--
1.8.1.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] net: fix comment above build_skb()
2013-07-23 15:39 [PATCH] net: fix comment above build_skb() Florian Fainelli
@ 2013-07-23 15:49 ` Eric Dumazet
2013-07-23 18:04 ` Florian Fainelli
0 siblings, 1 reply; 5+ messages in thread
From: Eric Dumazet @ 2013-07-23 15:49 UTC (permalink / raw)
To: Florian Fainelli; +Cc: davem, netdev
On Tue, 2013-07-23 at 16:39 +0100, Florian Fainelli wrote:
> build_skb() specifies that the data parameter must come from a kmalloc'd
> area, this is only true if frag_size equals 0, because then build_skb()
> will use kzsize(data) to figure out the actual data size. Update the
> comment to reflect that special condition.
>
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> net/core/skbuff.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 20e02d2..d3174db 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -309,7 +309,8 @@ EXPORT_SYMBOL(__alloc_skb);
> * @frag_size: size of fragment, or 0 if head was kmalloced
> *
> * Allocate a new &sk_buff. Caller provides space holding head and
> - * skb_shared_info. @data must have been allocated by kmalloc()
> + * skb_shared_info. @data must have been allocated by kmalloc() only if
> + * @frag_size is 0.
> * The return is the new skb buffer.
> * On a failure the return is %NULL, and @data is not freed.
> * Notes :
Hmm, why not explaining the other case ? (frag_size > 0)
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] net: fix comment above build_skb()
2013-07-23 15:49 ` Eric Dumazet
@ 2013-07-23 18:04 ` Florian Fainelli
2013-07-23 18:46 ` Ben Hutchings
2013-07-23 18:54 ` Eric Dumazet
0 siblings, 2 replies; 5+ messages in thread
From: Florian Fainelli @ 2013-07-23 18:04 UTC (permalink / raw)
To: Eric Dumazet; +Cc: David Miller, netdev
2013/7/23 Eric Dumazet <eric.dumazet@gmail.com>:
> On Tue, 2013-07-23 at 16:39 +0100, Florian Fainelli wrote:
>> build_skb() specifies that the data parameter must come from a kmalloc'd
>> area, this is only true if frag_size equals 0, because then build_skb()
>> will use kzsize(data) to figure out the actual data size. Update the
>> comment to reflect that special condition.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>> ---
>> net/core/skbuff.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> index 20e02d2..d3174db 100644
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -309,7 +309,8 @@ EXPORT_SYMBOL(__alloc_skb);
>> * @frag_size: size of fragment, or 0 if head was kmalloced
>> *
>> * Allocate a new &sk_buff. Caller provides space holding head and
>> - * skb_shared_info. @data must have been allocated by kmalloc()
>> + * skb_shared_info. @data must have been allocated by kmalloc() only if
>> + * @frag_size is 0.
>> * The return is the new skb buffer.
>> * On a failure the return is %NULL, and @data is not freed.
>> * Notes :
>
> Hmm, why not explaining the other case ? (frag_size > 0)
Sure, would something like:
"@data must have been allocated by kmalloc() if frag_size is 0,
otherwise any data buffer (vmalloc, DMA..) is suitable"
work for you?
--
Florian
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] net: fix comment above build_skb()
2013-07-23 18:04 ` Florian Fainelli
@ 2013-07-23 18:46 ` Ben Hutchings
2013-07-23 18:54 ` Eric Dumazet
1 sibling, 0 replies; 5+ messages in thread
From: Ben Hutchings @ 2013-07-23 18:46 UTC (permalink / raw)
To: Florian Fainelli; +Cc: Eric Dumazet, David Miller, netdev
On Tue, 2013-07-23 at 19:04 +0100, Florian Fainelli wrote:
> 2013/7/23 Eric Dumazet <eric.dumazet@gmail.com>:
> > On Tue, 2013-07-23 at 16:39 +0100, Florian Fainelli wrote:
> >> build_skb() specifies that the data parameter must come from a kmalloc'd
> >> area, this is only true if frag_size equals 0, because then build_skb()
> >> will use kzsize(data) to figure out the actual data size. Update the
> >> comment to reflect that special condition.
> >>
> >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> >> ---
> >> net/core/skbuff.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> >> index 20e02d2..d3174db 100644
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -309,7 +309,8 @@ EXPORT_SYMBOL(__alloc_skb);
> >> * @frag_size: size of fragment, or 0 if head was kmalloced
> >> *
> >> * Allocate a new &sk_buff. Caller provides space holding head and
> >> - * skb_shared_info. @data must have been allocated by kmalloc()
> >> + * skb_shared_info. @data must have been allocated by kmalloc() only if
> >> + * @frag_size is 0.
> >> * The return is the new skb buffer.
> >> * On a failure the return is %NULL, and @data is not freed.
> >> * Notes :
> >
> > Hmm, why not explaining the other case ? (frag_size > 0)
>
> Sure, would something like:
>
> "@data must have been allocated by kmalloc() if frag_size is 0,
> otherwise any data buffer (vmalloc, DMA..) is suitable"
The other case is that the buffer must have been allocated using the
page allocator directly. It will be freed using
put_page(virt_to_head_page(data)).
Using vmalloc() to allocate the buffer would definitely be incorrect.
Ben.
--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] net: fix comment above build_skb()
2013-07-23 18:04 ` Florian Fainelli
2013-07-23 18:46 ` Ben Hutchings
@ 2013-07-23 18:54 ` Eric Dumazet
1 sibling, 0 replies; 5+ messages in thread
From: Eric Dumazet @ 2013-07-23 18:54 UTC (permalink / raw)
To: Florian Fainelli; +Cc: David Miller, netdev
On Tue, 2013-07-23 at 19:04 +0100, Florian Fainelli wrote:
> Sure, would something like:
>
> "@data must have been allocated by kmalloc() if frag_size is 0,
> otherwise any data buffer (vmalloc, DMA..) is suitable"
>
Actually not, the other case must be a page frag, because we are going
to use get_page() and put_page() during skb lifetime.
netlink case is really special/hacky, because it makes sure those
get_page()/put_page() calls wont ever happen.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2013-07-23 15:39 [PATCH] net: fix comment above build_skb() Florian Fainelli
2013-07-23 15:49 ` Eric Dumazet
2013-07-23 18:04 ` Florian Fainelli
2013-07-23 18:46 ` Ben Hutchings
2013-07-23 18:54 ` Eric Dumazet
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