Hello, On Fri, Apr 08, 2011 at 05:43:16PM +0100, Stefan Hajnoczi wrote: > >> I think it would make sense to refresh the inode size on media change > >> so that even open file descriptors see the new size and a single > >> process cannot force a stale value for all other userspace processes > >> on the system. > > > > Hmmm... I don't know. Maybe we can but I'm not sure whether there's a > > good reason for it. cdrom is locked while opened after all. Are > > there actual problems? > > Yeah, sorry I didn't explain what the use case was. With QEMU you can > pass through the physical CD-ROM into the virtual machine. > > QEMU opens /dev/cdrom with O_NONBLOCK | O_RDONLY. The guest can test > if the medium is present and QEMU will do ioctl(fd, > CDROM_DRIVE_STATUS, CDSL_CURRENT). The guest can also lock the tray > and eject, again using the respective ioctls. Read operations are > serviced by performing a read on the file descriptor in QEMU. And > finally the medium size is queried by QEMU using lseek(fd, 0, > SEEK_END). > > Today QEMU cannot keep /dev/cdrom open across media change because it > will have an outdated inode size returned from lseek(fd, 0, SEEK_END). > But if the cdrom driver (or sr) refresh the inode size on media > change then there is no need to work around this from userspace. Hmmm... ISTR there was some discussion about changing inode size on the fly quite a while ago. I didn't follow the discussion but it seemed to have rather nasty/delicate implications. Jens, any ideas? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
