netdev - Re: [PATCH] Partially revert "net/smc: Add netlink net namespace support"

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Message-ID: <YgOM0dKMYGr8xeey@TonyMac-Alibaba>
Date:   Wed, 9 Feb 2022 17:43:45 +0800
From:   Tony Lu <tonylu@...ux.alibaba.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Karsten Graul <kgraul@...ux.ibm.com>, kuba@...nel.org,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] Partially revert "net/smc: Add netlink net namespace
 support"

On Wed, Feb 02, 2022 at 06:09:04AM +0300, Dmitry V. Levin wrote:
> The change of sizeof(struct smc_diag_linkinfo) by commit 79d39fc503b4
> ("net/smc: Add netlink net namespace support") introduced an ABI
> regression: since struct smc_diag_lgrinfo contains an object of
> type "struct smc_diag_linkinfo", offset of all subsequent members
> of struct smc_diag_lgrinfo was changed by that change.
> 
> As result, applications compiled with the old version
> of struct smc_diag_linkinfo will receive garbage in
> struct smc_diag_lgrinfo.role if the kernel implements
> this new version of struct smc_diag_linkinfo.
> 
> Fix this regression by reverting the part of commit 79d39fc503b4 that
> changes struct smc_diag_linkinfo.  After all, there is SMC_GEN_NETLINK
> interface which is good enough, so there is probably no need to touch
> the smc_diag ABI in the first place.
> 
> Fixes: 79d39fc503b4 ("net/smc: Add netlink net namespace support")
> Signed-off-by: Dmitry V. Levin <ldv@...linux.org>

Thank you and Karsten.

It was my negligence that caused the ABI incompatibility issue.
I will consider to fix it completely. And we are starting to build
smc-tools and other userspace test for potential ABI modifications.

Best regards,
Tony Lu