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Old 09-19-2006, 12:12 PM   #1
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Question Is this a bug, or a new feature?

I think I have found a bug in the low level read() code of the 2.6.9-34 kernel from RedHat, or maybe a new feature.

To summarize, reading of a file in the same process which opened it with a F_WRLCK will fail in 2.6.9-34 but not in the 2.4.21-27 kernel.

It fails only when the disk is a cached nfs mounted disk. It works as before on local disks, and disks mounted with "noac".

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

int main (int argc, char *argv[] )
   int f;

   int i;
   char buff[10] = "TestBuffer";
   struct flock fl;

   f = open(argv[1],O_RDWR|O_CREAT|O_EXCL,0666);
   fcntl(f,F_SETLK, &fl);      
   printf("read = %d\n",read(f,buff,10));
The program outputs "read = 0" on 2.6.9-34 when it cannot read from a file it opened with a F_WRLCK lock, the error condition. It will output "read = 10" always on 2.4.21-27 and when using a local disk like /tmp, or when using a disk mounted with a "noac". "read = 10" means things are working properly.

How do a report this bug? Or how do I determine if it is a bug or a new "feature"?

Last edited by zero_g; 09-21-2006 at 10:03 AM.
Old 09-19-2006, 01:07 PM   #2
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Please see;
Old 09-20-2006, 08:57 AM   #3
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How is the update related to the bug?

Thanks for the link, however, it is not apparent to me how this update from Red Hat relates to my problem with the NFS disks.


file, process, read, same

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