>The char * in the arguments of read is a user-space buffer pointer. It isn't actually a pointer at all. It's an address. People often run into trouble like yours because they don't grasp that. "char *" is an unfortunate choice of data type for this because it obscures that point and prevents the compiler from detecting errors. Some kernel code uses "long" instead, which is a much better choice. If Linux were like that, your code would have failed to compile rather than give you EFAULT (or worse) at run time. Actually ISTR Linux did get in the past few years some kind of typing scheme for user space addresses -- but we don't see it here. Does anyone know about that? A pointer is something that points to a variable. The usual implementations of C use memory to represent a variable and the address in some particular address space of that memory to represent a pointer. A more sophisticated implementation might include address space information in the pointer and then you truly could have a "char *" argument to ->read() and read into a user space buffer the same way you read into a kernel buffer. -- Bryan Henderson IBM Almaden Research Center San Jose CA Filesystems - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
