LINUX 设备驱动程序代码 2

While most of the source code printed in the book is part of real program files, a few of the examples are standalone excerpts I wrote out of my mind. Unfortunately, I managed to fit a pair of errors in these code lines. Page XXX ======== In chapter 9 ("Interrupt Handling"), in the section called "Going to Sleep Without Races", the code shown has a subtle bug. The correct implementation of the trick looks like the following: add_wait_queue(&short_queue, &wait); do { current->state = TASK_INTERRUPTIBLE; schedule(); } while ((short_head == short_tail) && !(current->signal & ~current->blocked) ); remove_wait_queue(&short_queue, &wait); if (current->signal & ~current->blocked) /* a signal arrived */ return -ERESTARTSYS; This is different from the version shown in the printed text as signal decoding must be performed *after* calling remove_wait_queue(). Page YYY ======== In chapter 17, in the section called "Using the New Interface", the ioctl() implementation shown includes a stupid mistake: "retval" is not initilized. A correct implementation is: int another_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg); { int retval = -EINVAL, size = _IOC_SIZE(cmd); if (_IOC_DIR(cmd) & _IOC_READ) { if (!access_ok(VERIFY_WRITE, (void *)arg, size)) retturn -EFAULT; } else if (_IOC_DIR(cmd) & _IOC_WRITE) { if (!access_ok(VERIFY_READ, (void *)arg, size)) return -EFAULT switch(cmd) { case NEW_GETVALUE: retval = __put_user(another_value,arg); break; case NEW_SETVALUE: retval = __get_user(another_value,arg); break; } return retval; } Another possibility is just stating "retval = 1" and leaving the code as shown, but I don't like the unadorned boolean value. Naturally, there are a lot of alternatives to this setup of ioctl(). ---------------------------------------------------------------------- The following notes are about two differences between my intentions, as stated in the printed book, and the actual outcome of the sample files as you find them on the ftp site. Allocating DMA memory ===================== In the section called "Allocating the DMA buffer", in chapter 13, I refer to an "allocator.c" module, which performs aggressive allocation. After using such a module in practice, I found that it didn't get reliable results, so I dropped it altogether. The implementation you find in the sample files (misc-modules/allocator.c) uses high memory to allocate the DMA buffer, in the way explained in the same section of chapter 13. misc-modules/README.allocator explains the issue to a finer detail. Decoding Oops messages ====================== The version of "oops" you find on the ftp site only decodes messages generated on the Intel platform. I didn't manage to find the time to implement it on the Alpha and the Sparc, as I intended to. As a matter of fact, Oops messages on RISC platforms include less information than Intel ones, and they are harder to use.