Re: [Qemu-devel] [RFC v3 PATCH 01/45] multi-process: memory: alloc RAM from file at offset

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Jag Raman (jag.raman@oracle.com) wrote:
> 
> 
> On 9/4/2019 4:11 AM, Dr. David Alan Gilbert wrote:
> > * Jagannathan Raman (jag.raman@oracle.com) wrote:
> > > Allow RAM MemoryRegion to be created from an offset in a file, instead
> > > of allocating at offset of 0 by default. This is needed to synchronize
> > > RAM between QEMU & remote process.
> > > This will be needed for the following patches.
> > > 
> > > Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> > > Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> > > Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> > > ---
> > >   exec.c                    | 11 +++++++----
> > >   include/exec/ram_addr.h   |  2 +-
> > >   include/qemu/mmap-alloc.h |  3 ++-
> > >   memory.c                  |  2 +-
> > >   util/mmap-alloc.c         |  7 ++++---
> > >   util/oslib-posix.c        |  2 +-
> > >   6 files changed, 16 insertions(+), 11 deletions(-)
> > 
> > I'm surprised this doesn't change something in
> > vhost-user.c:vhost_user_set_mem_table so that the vhost-user client
> > knows what it's mapping?
> 
> Hi Dave,
> 
> vhost-user does not use the functions addressed in this patch for
> mapping the RAM onto the remote process. It calls mmap() for this
> purpose (vu_set_mem_table_exec()).

It should at least check that the file it's sending over set-mem-table
has a 0 offset, otherwise things could get confused if someone tries
to run a vhost-user device on a system that's also running multi-process
(which should be a whole world of fun!)

dave

> Thanks!
> --
> Jag
> 
> > 
> > Dave
> > 
> > > diff --git a/exec.c b/exec.c
> > > index 3e78de3..b3f1aa9 100644
> > > --- a/exec.c
> > > +++ b/exec.c
> > > @@ -1885,6 +1885,7 @@ static void *file_ram_alloc(RAMBlock *block,
> > >                               ram_addr_t memory,
> > >                               int fd,
> > >                               bool truncate,
> > > +                            off_t offset,
> > >                               Error **errp)
> > >   {
> > >       MachineState *ms = MACHINE(qdev_get_machine());
> > > @@ -1936,7 +1937,8 @@ static void *file_ram_alloc(RAMBlock *block,
> > >       }
> > >       area = qemu_ram_mmap(fd, memory, block->mr->align,
> > > -                         block->flags & RAM_SHARED, block->flags & RAM_PMEM);
> > > +                         block->flags & RAM_SHARED, block->flags & RAM_PMEM,
> > > +                         offset);
> > >       if (area == MAP_FAILED) {
> > >           error_setg_errno(errp, errno,
> > >                            "unable to map backing store for guest RAM");
> > > @@ -2325,7 +2327,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
> > >   #ifdef CONFIG_POSIX
> > >   RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> > >                                    uint32_t ram_flags, int fd,
> > > -                                 Error **errp)
> > > +                                 off_t offset, Error **errp)
> > >   {
> > >       RAMBlock *new_block;
> > >       Error *local_err = NULL;
> > > @@ -2370,7 +2372,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> > >       new_block->used_length = size;
> > >       new_block->max_length = size;
> > >       new_block->flags = ram_flags;
> > > -    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
> > > +    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, offset,
> > > +                                     errp);
> > >       if (!new_block->host) {
> > >           g_free(new_block);
> > >           return NULL;
> > > @@ -2400,7 +2403,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> > >           return NULL;
> > >       }
> > > -    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
> > > +    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, 0, errp);
> > >       if (!block) {
> > >           if (created) {
> > >               unlink(mem_path);
> > > diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> > > index b7b2e60..15837a1 100644
> > > --- a/include/exec/ram_addr.h
> > > +++ b/include/exec/ram_addr.h
> > > @@ -164,7 +164,7 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> > >                                      Error **errp);
> > >   RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
> > >                                    uint32_t ram_flags, int fd,
> > > -                                 Error **errp);
> > > +                                 off_t offset, Error **errp);
> > >   RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> > >                                     MemoryRegion *mr, Error **errp);
> > > diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> > > index e786266..4f57985 100644
> > > --- a/include/qemu/mmap-alloc.h
> > > +++ b/include/qemu/mmap-alloc.h
> > > @@ -25,7 +25,8 @@ void *qemu_ram_mmap(int fd,
> > >                       size_t size,
> > >                       size_t align,
> > >                       bool shared,
> > > -                    bool is_pmem);
> > > +                    bool is_pmem,
> > > +                    off_t start);
> > >   void qemu_ram_munmap(int fd, void *ptr, size_t size);
> > > diff --git a/memory.c b/memory.c
> > > index 5d8c9a9..debed5e 100644
> > > --- a/memory.c
> > > +++ b/memory.c
> > > @@ -1622,7 +1622,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
> > >       mr->destructor = memory_region_destructor_ram;
> > >       mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
> > >                                              share ? RAM_SHARED : 0,
> > > -                                           fd, &err);
> > > +                                           fd, 0, &err);
> > >       mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
> > >       if (err) {
> > >           mr->size = int128_zero();
> > > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> > > index f7f177d..4b727bd 100644
> > > --- a/util/mmap-alloc.c
> > > +++ b/util/mmap-alloc.c
> > > @@ -86,7 +86,8 @@ void *qemu_ram_mmap(int fd,
> > >                       size_t size,
> > >                       size_t align,
> > >                       bool shared,
> > > -                    bool is_pmem)
> > > +                    bool is_pmem,
> > > +                    off_t start)
> > >   {
> > >       int flags;
> > >       int map_sync_flags = 0;
> > > @@ -147,7 +148,7 @@ void *qemu_ram_mmap(int fd,
> > >       offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
> > >       ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> > > -               flags | map_sync_flags, fd, 0);
> > > +               flags | map_sync_flags, fd, start);
> > >       if (ptr == MAP_FAILED && map_sync_flags) {
> > >           if (errno == ENOTSUP) {
> > > @@ -172,7 +173,7 @@ void *qemu_ram_mmap(int fd,
> > >            * we will remove these flags to handle compatibility.
> > >            */
> > >           ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
> > > -                   flags, fd, 0);
> > > +                   flags, fd, start);
> > >       }
> > >       if (ptr == MAP_FAILED) {
> > > diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> > > index fe0309c..f6a243f 100644
> > > --- a/util/oslib-posix.c
> > > +++ b/util/oslib-posix.c
> > > @@ -204,7 +204,7 @@ void *qemu_memalign(size_t alignment, size_t size)
> > >   void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
> > >   {
> > >       size_t align = QEMU_VMALLOC_ALIGN;
> > > -    void *ptr = qemu_ram_mmap(-1, size, align, shared, false);
> > > +    void *ptr = qemu_ram_mmap(-1, size, align, shared, false, 0);
> > >       if (ptr == MAP_FAILED) {
> > >           return NULL;
> > > -- 
> > > 1.8.3.1
> > > 
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> > 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK