question about pread() while reading /dev/sdb

question about pread() while reading /dev/sdb

[joso]

Hello, I'm porting tool from Linux envirmnment to Windows Cygwin.
I'm unable to get correct data from pread() while reading /dev/sdx
On Linux it works as expected, under Cygwin I receive uncorrect data.

I have isolated the problem with the following program:

#include  stdio.h
#include  sys/types.h
#include  sys/stat.h
#include  fcntl.h
#include  unistd.h

int main(int argc, char *argv[])
{
  unsigned char sbuff[512];
  int f1;
  f1=open(argv[1], O_RDWR);
  pread(f1, sbuff, 512, 0);
    for(int i=0; i 512; i++) printf("%x ",sbuff[i]);
  close(f1);
}

If the argument is regular file it works. But if the argument is /dev/sdb it does not provide correct data. The shell is run under Administrator permission.
Thank you for your opinion.
Josef

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: question about pread() while reading /dev/sdb

[Corinna Vinschen]

[-- Attachment #1: Type: text/plain, Size: 1150 bytes --]

On Jun  6 19:27, joso@post.cz wrote:
> Hello, I'm porting tool from Linux envirmnment to Windows Cygwin.
> I'm unable to get correct data from pread() while reading /dev/sdx
> On Linux it works as expected, under Cygwin I receive uncorrect data.
> 
> I have isolated the problem with the following program:
> 
> #include  stdio.h
> #include  sys/types.h
> #include  sys/stat.h
> #include  fcntl.h
> #include  unistd.h
> 
> int main(int argc, char *argv[])
> {
>   unsigned char sbuff[512];
>   int f1;
>   f1=open(argv[1], O_RDWR);
>   pread(f1, sbuff, 512, 0);
>     for(int i=0; i 512; i++) printf("%x ",sbuff[i]);
>   close(f1);
> }
> 
> If the argument is regular file it works. But if the argument is /dev/sdb it does not provide correct data. The shell is run under Administrator permission.
> Thank you for your opinion.

Cygwin's pread is only implemented for regular files at the moment,
for all other objects it returns -1 with errno set to ESPIPE.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]