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ivshmem: Implement shm=... with a memory backend 

ivshmem has its very own code to create and map shared memory.
Replace that with an implicitly created memory backend.  Reduces the
number of ways we create BAR 2 from three to two.

The memory-backend-file is currently available only with CONFIG_LINUX,
so this adds a second Linuxism to ivshmem (the other one is eventfd).
Should we ever need to make it portable to systems where
memory-backend-file can't be made to serve, we could create a
memory-backend-shmem that allocates memory with shm_open().

Bonus fix: shared memory files are now created with permissions 0655
instead of 0777.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1458066895-20632-32-git-send-email-armbru@redhat.com>
This commit is contained in:
Markus Armbruster 2016-03-15 19:34:46 +01:00
parent 08183c20b8
commit 5503e28504
1 changed files with 23 additions and 56 deletions
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79
hw/misc/ivshmem.c
View File

@ -26,6 +26,7 @@
#include "migration/migration.h"
#include "qemu/error-report.h"
#include "qemu/event_notifier.h"
#include "qom/object_interfaces.h"
#include "sysemu/char.h"
#include "sysemu/hostmem.h"
#include "qapi/visitor.h"
@ -369,31 +370,6 @@ static int check_shm_size(IVShmemState *s, int fd, Error **errp)
}
}
/* create the shared memory BAR when we are not using the server, so we can
* create the BAR and map the memory immediately */
static int create_shared_memory_BAR(IVShmemState *s, int fd, uint8_t attr,
Error **errp)
{
void * ptr;
ptr = mmap(0, s->ivshmem_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (ptr == MAP_FAILED) {
error_setg_errno(errp, errno, "Failed to mmap shared memory");
return -1;
}
memory_region_init_ram_ptr(&s->ivshmem, OBJECT(s), "ivshmem.bar2",
s->ivshmem_size, ptr);
qemu_set_ram_fd(memory_region_get_ram_addr(&s->ivshmem), fd);
vmstate_register_ram(&s->ivshmem, DEVICE(s));
memory_region_add_subregion(&s->bar, 0, &s->ivshmem);
/* region for shared memory */
pci_register_bar(PCI_DEVICE(s), 2, attr, &s->bar);
return 0;
}
static void ivshmem_add_eventfd(IVShmemState *s, int posn, int i)
{
memory_region_add_eventfd(&s->ivshmem_mmio,
@ -837,6 +813,23 @@ static void ivshmem_write_config(PCIDevice *pdev, uint32_t address,
}
}
static void desugar_shm(IVShmemState *s)
{
Object *obj;
char *path;
obj = object_new("memory-backend-file");
path = g_strdup_printf("/dev/shm/%s", s->shmobj);
object_property_set_str(obj, path, "mem-path", &error_abort);
g_free(path);
object_property_set_int(obj, s->ivshmem_size, "size", &error_abort);
object_property_set_bool(obj, true, "share", &error_abort);
object_property_add_child(OBJECT(s), "internal-shm-backend", obj,
&error_abort);
user_creatable_complete(obj, &error_abort);
s->hostmem = MEMORY_BACKEND(obj);
}
static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
{
IVShmemState *s = IVSHMEM(dev);
@ -915,6 +908,10 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
attr |= PCI_BASE_ADDRESS_MEM_TYPE_64;
}
if (s->shmobj) {
desugar_shm(s);
}
if (s->hostmem != NULL) {
MemoryRegion *mr;
@ -925,7 +922,7 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
vmstate_register_ram(mr, DEVICE(s));
memory_region_add_subregion(&s->bar, 0, mr);
pci_register_bar(PCI_DEVICE(s), 2, attr, &s->bar);
} else if (s->server_chr != NULL) {
} else {
IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
s->server_chr->filename);
@ -952,36 +949,6 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
error_setg(errp, "failed to initialize interrupts");
return;
}
} else {
/* just map the file immediately, we're not using a server */
int fd;
IVSHMEM_DPRINTF("using shm_open (shm object = %s)\n", s->shmobj);
/* try opening with O_EXCL and if it succeeds zero the memory
* by truncating to 0 */
if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
S_IRWXU|S_IRWXG|S_IRWXO)) > 0) {
/* truncate file to length PCI device's memory */
if (ftruncate(fd, s->ivshmem_size) != 0) {
error_report("could not truncate shared file");
}
} else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
error_setg(errp, "could not open shared file");
return;
}
if (check_shm_size(s, fd, errp) == -1) {
return;
}
create_shared_memory_BAR(s, fd, attr, &err);
if (err) {
error_propagate(errp, err);
return;
}
}
if (s->role_val == IVSHMEM_PEER) {