Hi
On Tue, Nov 24, 2020 at 3:54 PM Dr. David Alan Gilbert
<[email protected]> wrote:
>
> * [email protected] ([email protected]) wrote:
> > From: Marc-André Lureau <[email protected]>
> >
> > Undo the damage from commit 5f9ff1eff3 ("libvhost-user: Support tracking
> > inflight I/O in shared memory") which introduced glib dependency through
> > osdep.h inclusion.
> >
> > libvhost-user.c tries to stay free from glib usage.
> >
> > Use glibc memfd_create directly when available (assumed so when
> > MFD_ALLOW_SEALING is defined).
> >
> > Signed-off-by: Marc-André Lureau <[email protected]>
> > ---
> > contrib/libvhost-user/libvhost-user.c | 50 +++++++++++++++++++++++----
> > 1 file changed, 43 insertions(+), 7 deletions(-)
> >
> > diff --git a/contrib/libvhost-user/libvhost-user.c
> > b/contrib/libvhost-user/libvhost-user.c
> > index 1c1cfbf1e7..805521859d 100644
> > --- a/contrib/libvhost-user/libvhost-user.c
> > +++ b/contrib/libvhost-user/libvhost-user.c
> > @@ -42,8 +42,6 @@
> > #endif
> >
> > #include "qemu/atomic.h"
> > -#include "qemu/osdep.h"
> > -#include "qemu/memfd.h"
> >
> > #include "libvhost-user.h"
> >
> > @@ -1615,11 +1613,45 @@ vu_inflight_queue_size(uint16_t queue_size)
> > sizeof(uint16_t), INFLIGHT_ALIGNMENT);
> > }
> >
> > +#ifdef MFD_ALLOW_SEALING
> > +static void *
> > +memfd_alloc(const char *name, size_t size, unsigned int flags, int *fd)
> > +{
> > + void *ptr;
> > + int ret;
> > +
> > + *fd = memfd_create(name, MFD_ALLOW_SEALING);
> > + if (*fd < 0) {
> > + return NULL;
> > + }
> > +
> > + ret = ftruncate(*fd, size);
>
> Do you need to do any of the page alignment?
We don't do any in util/memfd.c, I don't see an explicit requirement
in memfd_create(). (however, util/memfd.c did check power of 2 for
hugetlb usage, but this isn't necessary here)
On mmap(), "if addr is NULL, then the kernel chooses the (page-aligned) address"
>
> > + if (ret < 0) {
> > + close(*fd);
> > + return NULL;
> > + }
> > +
> > + ret = fcntl(*fd, F_ADD_SEALS, F_SEAL_GROW | F_SEAL_SHRINK |
> > F_SEAL_SEAL);
>
> I think you'd intended to use the 'flags' parameter there.
indeed, thanks
>
> > + if (ret < 0) {
> > + close(*fd);
> > + return NULL;
> > + }
> > +
> > + ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, *fd, 0);
> > + if (ptr == MAP_FAILED) {
> > + close(*fd);
> > + return NULL;
> > + }
> > +
> > + return ptr;
> > +}
> > +#endif
> > +
> > static bool
> > vu_get_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
> > {
> > - int fd;
> > - void *addr;
> > + int fd = -1;
> > + void *addr = NULL;
> > uint64_t mmap_size;
> > uint16_t num_queues, queue_size;
> >
> > @@ -1637,9 +1669,13 @@ vu_get_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
> >
> > mmap_size = vu_inflight_queue_size(queue_size) * num_queues;
> >
> > - addr = qemu_memfd_alloc("vhost-inflight", mmap_size,
> > - F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL,
> > - &fd, NULL);
> > +#ifdef MFD_ALLOW_SEALING
> > + addr = memfd_alloc("vhost-inflight", mmap_size,
> > + F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL,
> > + &fd);
> > +#else
> > + vu_panic(dev, "Not implemented: memfd support is missing");
>
> Should there be an ifdef somewhere on the declared features, so it
> doesn't get this far because it wont negotiate the feature?
Sealing grow/shrink came together with memfd, it was one of the main
selling point. I assume if MFD_ALLOW_SEALING is defined, we have
memfd_create and basic libc defines. But yes, if we want to handle
weird corner cases, we should add more ifdef-ry. I'd pass for now.
thanks
>
> Dave
>
> > +#endif
> >
> > if (!addr) {
> > vu_panic(dev, "Failed to alloc vhost inflight area");
> > --
> > 2.29.0
> >
> --
> Dr. David Alan Gilbert / [email protected] / Manchester, UK
>
