Reply-To: jesper.pedersen@redhat.com
Subject: Re: pread() and pwrite()
From: Jesper Pedersen <jesper.pedersen@redhat.com>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@2ndquadrant.com>,
 Magnus Hagander <magnus@hagander.net>, Oskari Saarenmaa <os@ohmu.fi>,
 Pg Hackers <pgsql-hackers@postgresql.org>,
 Tobias Oberstein <tobias.oberstein@gmail.com>
References: <20181105155918.jg36uj4rtnxwqtzt@alvherre.pgsql>
 <1791.1541438632@sss.pgh.pa.us>
 <CAEepm=1GmuQ---ZDmmDzU6uS0QF==PeD1N-XLY7pSfndxTpnfQ@mail.gmail.com>
 <856530e2-260d-1d61-ec18-595778868a1b@redhat.com>
 <CAEepm=0+GizsKRRd=7wrL0n8VMKadR0=o99VWiXD58oJyJOUCQ@mail.gmail.com>
 <cb062f4d-55b8-28be-b55f-2e593a3b3755@redhat.com>
Organization: Red Hat
Message-ID: <20f9e0dc-0638-98df-abfc-92002d688bbd@redhat.com>
Date: Wed, 7 Nov 2018 09:03:27 -0500
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Hi,

On 11/7/18 7:26 AM, Jesper Pedersen wrote:
> On 11/6/18 4:04 PM, Thomas Munro wrote:
>> On Wed, Nov 7, 2018 at 4:42 AM Jesper Pedersen
>> Thanks!  Pushed.  I'll keep an eye on the build farm to see if
>> anything breaks on Cygwin or some other frankenOS.
>>
> 
> There is [1] on Andres' skink setup. Looking.
> 

Attached is a reproducer.

Adding the memset() command for the page makes valgrind happy.

Thoughts on how to proceed with this ? The report in [1] shows that 
there are a number of call sites where the page(s) aren't fully initialized.

[1] 
https://www.postgresql.org/message-id/3fe1e38a-fb70-6260-9300-ce67ede21c32%40redhat.com

Best regards,
  Jesper

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, const char* argv[])
{
   FILE* f;
   int fd;
   void* m;
   ssize_t written;

   f = fopen("test.bin", "w+");
   if (f == NULL)
   {
      printf("Cannot open file\n");
      exit(0);
   }
   fd = fileno(f);
   m = malloc((size_t)8192);
   // memset(m, 0, (size_t)8192); <-- will make valgrind succeed

   written = pwrite(fd, m, (size_t)8192, (off_t)0);
   
   printf("Written: %i\n", written);

   free(m);
   fclose(f);
   
   return 0;
}

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