On Tue, Sep 29, 2015 at 11:25:04AM -0400, Marc-André Lureau wrote: > > > ----- Original Message ----- > > On Thu, Aug 06, 2015 at 02:40:39PM +0200, marcandre.lur...@redhat.com wrote: > > > From: Marc-André Lureau <marcandre.lur...@redhat.com> > > > > > > Add qemu_memfd_alloc/free() helpers. > > > > > > The function helps to allocate and seal a memfd, and implements an > > > open/unlink/mmap fallback for system that do not support memfd. > > > > > > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> > > > --- > > > include/qemu/memfd.h | 4 +++ > > > util/memfd.c | 74 > > > ++++++++++++++++++++++++++++++++++++++++++++++++++-- > > > 2 files changed, 76 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h > > > index 8b1fe6a..950fb88 100644 > > > --- a/include/qemu/memfd.h > > > +++ b/include/qemu/memfd.h > > > @@ -17,4 +17,8 @@ > > > #define F_SEAL_WRITE 0x0008 /* prevent writes */ > > > #endif > > > > > > +void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, > > > + int *fd); > > > +void qemu_memfd_free(void *ptr, size_t size, int fd); > > > + > > > #endif /* QEMU_MEMFD_H */ > > > diff --git a/util/memfd.c b/util/memfd.c > > > index a98d57e..8b2b785 100644 > > > --- a/util/memfd.c > > > +++ b/util/memfd.c > > > @@ -27,6 +27,14 @@ > > > > > > #include "config-host.h" > > > > > > +#include <glib.h> > > > +#include <glib/gprintf.h> > > > + > > > +#include <stdio.h> > > > +#include <stdlib.h> > > > +#include <fcntl.h> > > > +#include <sys/mman.h> > > > + > > > #include "qemu/memfd.h" > > > > > > #ifdef CONFIG_MEMFD > > > @@ -44,13 +52,75 @@ > > > #define MFD_ALLOW_SEALING 0x0002U > > > #endif > > > > > > -static inline int memfd_create(const char *name, unsigned int flags) > > > +static int memfd_create(const char *name, unsigned int flags) > > > { > > > return syscall(__NR_memfd_create, name, flags); > > > } > > > #else /* !LINUX */ > > > -static inline int memfd_create(const char *name, unsigned int flags) > > > +static int memfd_create(const char *name, unsigned int flags) > > > { > > > return -1; > > > } > > > #endif > > > + > > > +void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, > > > + int *fd) > > > +{ > > > + void *ptr; > > > + int mfd; > > > + > > > + mfd = memfd_create(name, MFD_ALLOW_SEALING|MFD_CLOEXEC); > > > > > > Hmm. Does this interact correctly with the -mem-prealloc flag? > > It's unrelated imho. It's helper here. > > In the rest of the series, it's used at runtime when migrating with variable > size (today code doesn't prealloc that either)
Yes but I think this means it will fault on access even if user requested -realtime mlock=on. > > > > > + if (mfd != -1) { > > > + if (ftruncate(mfd, size) == -1) { > > > > Any limitations on size? > > not that I know (reading memfd_create) > > > > > > + perror("ftruncate"); > > > + close(mfd); > > > + return NULL; > > > + } > > > + > > > + if (fcntl(mfd, F_ADD_SEALS, seals) == -1) { > > > + perror("fcntl"); > > > + close(mfd); > > > + return NULL; > > > + } > > > + } else { > > > + const char *tmpdir = getenv("TMPDIR"); > > > + gchar *fname; > > > + > > > + tmpdir = tmpdir ? tmpdir : "/tmp"; > > > + > > > + fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); > > > > This means there's now work to be done to set up selinux > > to allow QEMU creating memfd under /tmp. > > doesn't sound unreasonable to me > > > > > Maybe it's better to just fail gracefully for now. > > it's a fallback, but sure we can remove it and add it back later if needed > > > > + mfd = mkstemp(fname); > > > + unlink(fname); > > > + g_free(fname); > > > + > > > + if (mfd == -1) { > > > + perror("mkstemp"); > > > + return NULL; > > > + } > > > + > > > + if (ftruncate(mfd, size) == -1) { > > > + perror("ftruncate"); > > > + close(mfd); > > > + return NULL; > > > + } > > > + } > > > + > > > + ptr = mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, mfd, 0); > > > > Pls add space around | here and elsewhere. > > > > ok > > > > > + if (ptr == MAP_FAILED) { > > > + perror("mmap"); > > > + close(mfd); > > > + return NULL; > > > + } > > > + > > > + *fd = mfd; > > > + return ptr; > > > +} > > > + > > > +void qemu_memfd_free(void *ptr, size_t size, int fd) > > > +{ > > > + if (ptr) { > > > + munmap(ptr, size); > > > + } > > > + > > > + close(fd); > > > > I notice you close fd unconditionally, but it's only returned > > on success above. So this will close an uninitialized one? > > Ok, I'll add a -1 check Will only work well if you set *fd to -1 on error above ... -- MST