Commit 5503e285 authored by Markus Armbruster's avatar Markus Armbruster
Browse files

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: default avatarMarkus Armbruster <armbru@redhat.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <1458066895-20632-32-git-send-email-armbru@redhat.com>
parent 08183c20

hw/misc/ivshmem.c

+23 −56
Original line number Diff line number Diff line
@@ -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) {