linux-kernel - RE: [PATCH 1/1] selftest/net: fix FILE

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Date:   Fri, 3 Aug 2018 11:12:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'maninder1.s@...sung.com'" <maninder1.s@...sung.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "shuahkh@....samsung.com" <shuahkh@....samsung.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        PANKAJ MISHRA <pankaj.m@...sung.com>,
        AMIT SAHRAWAT <a.sahrawat@...sung.com>,
        Vaneet Narang <v.narang@...sung.com>
Subject: RE: [PATCH 1/1] selftest/net: fix FILE_SIZE for 32 bit architecture.

From: Maninder Singh
> Sent: 03 August 2018 04:32
> >On 08/02/2018 03:31 AM, Maninder Singh wrote:
> >> FILE_SZ is defined as (1UL << 35), it will overflow
> >> for 32 bit system and logic will break.
> >>
> >> Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
> >> Signed-off-by: Vaneet Narang <v.narang@...sung.com>
> >> ---
> >>  tools/testing/selftests/net/tcp_mmap.c | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c
> >> index e8c5dff..1d6ca12 100644
> >> --- a/tools/testing/selftests/net/tcp_mmap.c
> >> +++ b/tools/testing/selftests/net/tcp_mmap.c
> >> @@ -85,7 +85,7 @@
> >>  #define MSG_ZEROCOPY    0x4000000
> >>  #endif
> >>
> >> -#define FILE_SZ (1UL << 35)
> >> +#define FILE_SZ (1ULL << 35)
> 
> ...
> ...
> >> @@ -431,7 +431,7 @@ int main(int argc, char *argv[])
> >>                  zflg = 0;
> >>          }
> >>          while (total < FILE_SZ) {
> >> -                long wr = FILE_SZ - total;
> >> +                unsigned long long wr = FILE_SZ - total;
> >>
> >>                  if (wr > chunk_size)
> >>                          wr = chunk_size;
> >>
> >
> >What about using more conventional size_t instead of "unsigned long long" ?
> 
> size_t is also equivalent to unsigned long and it will not hold value of (1 << 35) for 32 bit system.
> So we can do two things.

Wouldn't the 'correct' type be off_t ?
In any case, IIRC, you have to do really horrid things in Linux to
access files larger than 2G on 32bit systems.

	David

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