All of lore.kernel.org
 help / color / mirror / Atom feed
From: Steven Ting <steventing@realtek.com>
To: "johannes.berg@intel.com" <johannes.berg@intel.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Subject: Is the extra_tx_headroom guarenteed ?
Date: Mon, 7 Jun 2021 03:17:02 +0000	[thread overview]
Message-ID: <f045bc11c75e4603bf58f3d596448c7e@realtek.com> (raw)

Johannes and all mac80211 gurus,

We encountered a problem that we use the extra_tx_headroom to reserve the headroom
which we put the txdesc in.

Current workaround is that we check our needed headroom size by skb_headroom()
in the driver layer.

Is extra_tx_headroom in struct ieee80211_hw always guaranteed?
The header file describes:
* @extra_tx_headroom: headroom to reserve in each transmit skb
*      for use by the driver (e.g. for transmit headers.)

But when the skb goes through the ieee80211_amsdu_realloc_pad(), it does not
take care of the extra_tx_headroom, i.e. the original reserved headroom might be
eaten.

Does the ieee80211_amsdu_realloc_pad() lacks some check for extra_tx_headroom
or the extra_tx_headroom in mac80211 is not guaranteed?

Furthermore, for the packet that would not be aggregate in A-MSDU and ndev->needed_headroom
is not guaranteed, in this case whether mac80211 layer still guarantee the extra_tx_headroom ?

Or mac80211 only guarantees the headroom of the skb which is built by itself ?

Steven

             reply	other threads:[~2021-06-07  3:17 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-07  3:17 Steven Ting [this message]
2021-06-10 20:14 ` Is the extra_tx_headroom guarenteed ? Johannes Berg
2021-08-16  8:56   ` Pkshih

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f045bc11c75e4603bf58f3d596448c7e@realtek.com \
    --to=steventing@realtek.com \
    --cc=johannes.berg@intel.com \
    --cc=linux-wireless@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.