Re: [dpdk-dev] [PATCH v5 19/26] app/testpmd: add item raw to flow command

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

Hi Wei,

On Thu, May 11, 2017 at 06:53:52AM +0000, Zhao1, Wei wrote:
> Hi, Adrien
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Adrien Mazarguil
> > Sent: Wednesday, December 21, 2016 10:52 PM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH v5 19/26] app/testpmd: add item raw to flow
> > command
> > 
> > Matches arbitrary byte strings with properties:
> > 
> > - relative: look for pattern after the previous item.
> > - search: search pattern from offset (see also limit).
> > - offset: absolute or relative offset for pattern.
> > - limit: search area limit for start of pattern.
> > - length: pattern length.
> > - pattern: byte string to look for.
> > 
> > Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
> > Acked-by: Olga Shern <olgas@mellanox.com>
[...]
> #define  ITEM_RAW_PATTERN_SIZE 36
> 
> The size of NIC i350 flex byte filter can accommodate the max length size of 128 byte, and the reason to 
> Define it as 36 is ?If it is the max length of pattern, maybe 128  is more appropriate? 
> Maybe I have not understand your purpose.
> 
> Thank you.

It's more or less an arbitrary compromise due to various limitations.

Once parsed, the result of an entire command is stored in a fixed buffer of
size CMDLINE_PARSE_RESULT_BUFSIZE (8192). Each parsed token ends up
somewhere in that buffer.

Each flow item always consumes sizeof(struct rte_flow_item) + sizeof(struct
rte_flow_item_xxx) * 3 (spec, last and mask) + alignment constraints.

For the raw item, this makes at least:

 (sizeof(rte_flow_item) +
  (sizeof(rte_flow_item_raw) + ITEM_RAW_PATTERN_SIZE) * 3)
 /* (32 + (12 + 36) * 3) => 176 bytes */

Because space is always consumed regardless of the size of the byte string
to match for implementation reasons, there is a chance to fill the buffer
too quickly with a larger ITEM_RAW_PATTERN_SIZE.

Also, this does not prevent users from specifying larger raw patterns (even
larger than 128) by combining them, e.g.:

 flow create 0
    pattern eth / raw relative is 1 pattern is foobar /
       raw relative is 1 pattern is barbaz / end
    actions queue index 42 / end

Such a pattern ends up matching a single "foobarbarbaz" string.

To summarize, it is only due to testpmd limitations. Even without PMD
support for combination, the current ability to provide 36 bytes of raw data
to match per specified item is plenty to validate basic functionality. We'll
improve testpmd eventually.

-- 
Adrien Mazarguil
6WIND