Am 19.06.2012 17:46, schrieb Eric Blake: > On 06/14/2012 09:55 AM, Corey Bryant wrote: > >> This patch series adds the pass-fd QMP monitor command, which allows >> an fd to be passed via SCM_RIGHTS, and returns the received file >> descriptor. Support is also added to the block layer to allow QEMU >> to dup the fd when the filename is of the /dev/fd/X format. This >> is useful if MAC policy prevents QEMU from opening specific types >> of files. > > Something to think about on how this will interact with Jeff's work on > block-commit. That is an interface where qemu must reopen backing files > which were previously O_RDONLY to now be O_RDWR. By default (when > open() is supported in qemu, and qemu is using the actual file name), > this means 'block-commit' works without needing any fd names. But with > this new fd-passing approach, a file originally opened as O_RDONLY > /dev/fd/21 will need to be reopened, but the reopened fd will (likely) > not be 21. In other words, we need to make sure 'block-commit' supports > the ability to pass in optional arguments that specify the file name of > the backing file to be reopened, so that libvirt can pass in O_RDWR fds > to replace the existing O_RDONLY fd, and be aware that the /dev/fd/nn > naming of the reopen will be different. Adding an extra argument to each command that reopens (as in bdrv_reopen(), i.e. changes flags) internally is one option. In my opinion not a particularly nice one, though. Maybe it's better to have a monitor command that just prepares a reopen and means "for the next reopen of /dev/fd/42, the passed FD will have the right flags (if it hasn't, the reopen will fail)". We can use dup2() to keep the "name" stable. Kevin -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list