Re: [dpdk-dev] [PATCH] igb_uio: use macros for array size calculation

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Thursday, March 03, 2016 5:35 PM
> To: Ananyev, Konstantin; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] igb_uio: use macros for array size calculation
> 
> On 3/3/2016 5:25 PM, Ananyev, Konstantin wrote:
> >
> >
> >> -----Original Message-----
> >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ferruh Yigit
> >> Sent: Thursday, March 03, 2016 5:08 PM
> >> To: dev@dpdk.org
> >> Subject: [dpdk-dev] [PATCH] igb_uio: use macros for array size calculation
> >>
> >> Minor code cleanup.
> >> Remove array size calculations and remove unnecessary assignment.
> >>
> >> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
> >> ---
> >>  lib/librte_eal/linuxapp/igb_uio/igb_uio.c | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> >> index 3374e44..563c57b 100644
> >> --- a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> >> +++ b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> >> @@ -58,7 +58,7 @@ struct rte_uio_pci_dev {
> >>  	enum rte_intr_mode mode;
> >>  };
> >>
> >> -static char *intr_mode = NULL;
> >> +static char *intr_mode;
> >>  static enum rte_intr_mode igbuio_intr_mode_preferred = RTE_INTR_MODE_MSIX;
> >>
> >>  /* sriov sysfs */
> >> @@ -332,7 +332,7 @@ igbuio_pci_setup_iomem(struct pci_dev *dev, struct uio_info *info,
> >>  	unsigned long addr, len;
> >>  	void *internal_addr;
> >>
> >> -	if (sizeof(info->mem) / sizeof(info->mem[0]) <= n)
> >> +	if (n >= MAX_UIO_MAPS)
> >
> > Why using hardcoded value is better than sizeof()?
> > As I can see below there is a macro ARRAY_SIZE, why not to use it here then?
> 
> Both are valid, but in uio (uio_driver.h) "mem" array defined as:
>  struct uio_mem          mem[MAX_UIO_MAPS];

Yep, so if both are valid, why to change it a the first place? :)

> 
> So we already know the size of the array, and it is exposed to us, why
> need to calculate. Is there any benefit of calculating it?

if in future definition of the mem[] would change to let say:
struct uio_mem   mem[X]
your code would still be valid, and no need to update it. 
Konstantin

> 
> Thanks,
> ferruh