[Qemu-devel] [PATCH v4] ivshmem: allow the sharing of hugepages

[Pavel Fedin]

This patch permits to share memory areas that do not specifically belong to
/dev/shm. In such case, the file must be already present when launching qemu.
A new parameter 'file' has been added to specify the file to use.

A use case for this patch is sharing huge pages available through a
hugetlbfs mountpoint.

Signed-off-by: Damien Millescamps <address@hidden>
Signed-off-by: Pavel Fedin <address@hidden>
---
 2 years passed since the last review of this, and the original author never 
came back. So i decided
to pick up this work because my project is interested in this feature. I am 
keeping patch version
numbering, but the original changelog was lost.
 Relevant thread here: 
https://lists.gnu.org/archive/html/qemu-trivial/2013-09/msg00148.html

v3 => v4:
- Fixed documentation and wordings according to the last review
- Report also actual error messages
- Added missing exit()
- Fixed up code style according to latest checkpatch rules

---
 docs/specs/ivshmem_device_spec.txt |  7 ++--
 hw/misc/ivshmem.c                  | 67 +++++++++++++++++++++++++-------------
 2 files changed, 50 insertions(+), 24 deletions(-)

diff --git a/docs/specs/ivshmem_device_spec.txt 
b/docs/specs/ivshmem_device_spec.txt
index 667a862..8b108e7 100644
--- a/docs/specs/ivshmem_device_spec.txt
+++ b/docs/specs/ivshmem_device_spec.txt
@@ -4,8 +4,11 @@ Device Specification for Inter-VM shared memory device
 
 The Inter-VM shared memory device is designed to share a region of memory to
 userspace in multiple virtual guests.  The memory region does not belong to any
-guest, but is a POSIX memory object on the host.  Optionally, the device may
-support sending interrupts to other guests sharing the same memory region.
+guest, but is a either a POSIX memory object or a mmap'd file (for instance,
+hugepage-backed file) on the host.
+
+Optionally, the device may support sending interrupts to other guests sharing
+the same memory region.
 
 
 The Inter-VM PCI device
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index cc76989..999ed7d 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -100,9 +100,10 @@ typedef struct IVShmemState {
 
     Error *migration_blocker;
 
-    char * shmobj;
-    char * sizearg;
-    char * role;
+    char *shmobj;
+    char *fileobj;
+    char *sizearg;
+    char *role;
     int role_val;   /* scalar to avoid multiple string comparisons */
 } IVShmemState;
 
@@ -769,9 +770,9 @@ static int pci_ivshmem_init(PCIDevice *dev)
         /* if we get a UNIX socket as the parameter we will talk
          * to the ivshmem server to receive the memory region */
 
-        if (s->shmobj != NULL) {
+        if (s->shmobj != NULL || s->fileobj != NULL) {
             error_report("WARNING: do not specify both 'chardev' "
-                         "and 'shm' with ivshmem");
+                         "and 'shm' or 'file' with ivshmem");
         }
 
         IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
@@ -797,28 +798,49 @@ static int pci_ivshmem_init(PCIDevice *dev)
     } else {
         /* just map the file immediately, we're not using a server */
         int fd;
+        int is_shm = !!(s->shmobj != NULL);
+        int is_file = !!(s->fileobj != NULL);
 
-        if (s->shmobj == NULL) {
-            error_report("Must specify 'chardev' or 'shm' to ivshmem");
+        if (!(is_shm ^ is_file)) {
+            error_report("Must specify one of 'chardev', 'shm' or 'file' "
+                         "to ivshmem");
             exit(1);
         }
 
-        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");
+        if (is_shm) {
+            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 */
+            fd = shm_open(s->shmobj, O_CREAT|O_RDWR|O_EXCL,
+                          S_IRWXU|S_IRWXG|S_IRWXO);
+            if (fd > 0) {
+                /* truncate file to length PCI device's memory */
+                if (ftruncate(fd, s->ivshmem_size) != 0) {
+                    error_report("could not truncate shared file: %s",
+                                 strerror(errno));
+                    exit(1);
+                }
+            } else {
+                fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
+                              S_IRWXU|S_IRWXG|S_IRWXO);
+                if (fd < 0) {
+                    error_report("could not open shared file: %s",
+                                 strerror(errno));
+                    exit(1);
+                }
+            }
+        } else {
+            IVSHMEM_DPRINTF("using open (file object = %s)\n", s->fileobj);
+
+            /* try opening a mmap's file. This file must have been previously
+             * created on the host */
+            fd = open(s->fileobj, O_RDWR);
+            if (fd < 0) {
+                error_report("ivshmem: could not open file: %s\n",
+                             strerror(errno));
+                exit(-1);
             }
-
-        } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
-                        S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
-            error_report("could not open shared file");
-            exit(1);
-
         }
 
         if (check_shm_size(s, fd) == -1) {
@@ -856,6 +878,7 @@ static Property ivshmem_properties[] = {
     DEFINE_PROP_BIT("ioeventfd", IVShmemState, features, IVSHMEM_IOEVENTFD, 
false),
     DEFINE_PROP_BIT("msi", IVShmemState, features, IVSHMEM_MSI, true),
     DEFINE_PROP_STRING("shm", IVShmemState, shmobj),
+    DEFINE_PROP_STRING("file", IVShmemState, fileobj),
     DEFINE_PROP_STRING("role", IVShmemState, role),
     DEFINE_PROP_UINT32("use64", IVShmemState, ivshmem_64bit, 1),
     DEFINE_PROP_END_OF_LIST(),
-- 
1.9.5.msysgit.0