netdev - Re: [PATCH 06/39] net/socket.c: switch to CLASS(fd)

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Message-ID: <20240807-erbarmen-getextet-77b673347599@brauner>
Date: Wed, 7 Aug 2024 12:13:16 +0200
From: Christian Brauner <brauner@...nel.org>
To: viro@...nel.org
Cc: linux-fsdevel@...r.kernel.org, amir73il@...il.com, bpf@...r.kernel.org, 
	cgroups@...r.kernel.org, kvm@...r.kernel.org, netdev@...r.kernel.org, 
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 06/39] net/socket.c: switch to CLASS(fd)

On Tue, Jul 30, 2024 at 01:15:52AM GMT, viro@...nel.org wrote:
> From: Al Viro <viro@...iv.linux.org.uk>
> 
> 	I strongly suspect that important part in sockfd_lookup_light()
> is avoiding needless file refcount operations, not the marginal reduction
> of the register pressure from not keeping a struct file pointer in
> the caller.
> 
> 	If that's true, we should get the same benefits from straight
> fdget()/fdput().  And AFAICS with sane use of CLASS(fd) we can get a
> better code generation...
> 
> 	Would be nice if somebody tested it on networking test suites
> (including benchmarks)...
> 
> 	sockfd_lookup_light() does fdget(), uses sock_from_file() to
> get the associated socket and returns the struct socket reference to
> the caller, along with "do we need to fput()" flag.  No matching fdput(),
> the caller does its equivalent manually, using the fact that sock->file
> points to the struct file the socket has come from.
> 
> 	Get rid of that - have the callers do fdget()/fdput() and
> use sock_from_file() directly.  That kills sockfd_lookup_light()
> and fput_light() (no users left).
> 
> 	What's more, we can get rid of explicit fdget()/fdput() by
> switching to CLASS(fd, ...) - code generation does not suffer, since
> now fdput() inserted on "descriptor is not opened" failure exit
> is recognized to be a no-op by compiler.
> 
> 	We could split that commit in two (getting rid of sockd_lookup_light()
> and switch to CLASS(fd, ...)), but AFAICS it ends up being harder to read
> that way.
> 
> [conflicts in a couple of functions]
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---

Reviewed-by: Christian Brauner <brauner@...nel.org>