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Message-ID: <alpine.LNX.2.21.1810161014080.10@nippy.intranet>
Date: Tue, 16 Oct 2018 10:52:26 +1100 (AEDT)
From: Finn Thain <fthain@...egraphics.com.au>
To: Hannes Reinecke <hare@...e.de>
cc: "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Michael Schmitz <schmitzmic@...il.com>,
linux-scsi@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] esp_scsi: De-duplicate PIO routines
On Mon, 15 Oct 2018, Hannes Reinecke wrote:
> >
> > In the case of send_cmd_residual, that would mean a second #ifdef
> > added to esp_data_bytes_sent() where it gets used. I'm happy to comply
> > but I fear that all these #ifdefs may harm readability...
> >
> > There are already other variables in struct esp that may go unused,
> > such as dma_regs, that don't have #ifdefs to elide them. Are these
> > also problematic in some way?
> >
> The unused fields in the struct are not so much an issue; in fact, it
> rather complicated things when having individual fields in the struct
> surrounded by CONFIG_XXX, as then the order of the fields would change
> depending on the configuration. Which makes it really hard to debug ..
>
True enough. We agree that this #ifdef is undesirable. And yet when I
tried it, I found an unexpected readability benefit to your suggestion:
#ifdef CONFIG_SCSI_ESP_PIO
u8 __iomem *fifo_reg;
int send_cmd_error;
u32 send_cmd_residual;
#endif
This grouping does help convey the purpose of these struct members, even
though the #ifdef is meant for the compiler not for the human reader.
So maybe it makes sense to group these definitions (they are all the same
size):
/* These are used by esp_scsi_send_pio_cmd() */
u8 __iomem *fifo_reg;
int send_cmd_error;
u32 send_cmd_residual;
> However, the function declaration really is a worry, as the actual
> function body only exists when the config option is enabled. So either
> add a dummy function or surround the function declaration by
> CONFIG_ESP_PIO.
> Otherwise I think Dan Carpenter and the likes are guaranteed to send you
> a nice mail complaining about this ...
>
Do static checkers really complain about this? I think the validity of an
extern can't be known until the final linkage is done.
At that point the checker may complain that no compilation unit references
a symbol in a header.
But this would lead to false positives where a header file is shared by
separate programs which share library code but not macros.
--
> Cheers,
>
> Hannes
>
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