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clinuxfile-handlingfstat

fstat() return 0, with file size 0 and errno 11

I'm trying the following thing in my code:-

{

   int y,n_bytes;

   struct stat temp_data;

   y = fstat(netdev->queue_fd[class_id],&temp_data);
   printf("Success - %d , size -> %lld , Error- %d \n",y,temp_data.st_size,errno);
   n_bytes = write(netdev->queue_fd[class_id],buffer->data,buffer->size);
   y = fstat(netdev->queue_fd[class_id],&temp_data);
   printf("After write Success - %d , size -> %lld , Error- %d and the value of n_bytes is - %d ",y,temp_data.st_size,errno,n_bytes);

}

and the output that I'm getting is :-

Success - 0, size -> 0 , Error - 11 
After write Success - 0, size -> 0, Error - 11 and the value of n_bytes is - 1526

What is the reason behind the size being 0 and the error number 11?? Is there any other way to get the size of the file??

Note: here Netdev->queue_fd[class_id] is a file descriptor. The value of n_bytes is varying in between {41,1514,66,..} in different calls. (Always greater than 0)

thanks

Solution

  • Netdev->queue_fd[class_id] is a file descriptor of

    • Regular file or
    • Any sys/fs entry or
    • Char/Block/Network device file?

    if it is not a regular file then its size will not be updated after write command.

    check file tyeps by S_ISREG()