16.09.2013 17:46, Damien Millescamps wrote:
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 <damien.millesca...@6wind.com>
---
docs/specs/ivshmem_device_spec.txt | 5 ++-
hw/misc/ivshmem.c | 52 +++++++++++++++++++++++------------
2 files changed, 37 insertions(+), 20 deletions(-)
diff --git a/docs/specs/ivshmem_device_spec.txt
b/docs/specs/ivshmem_device_spec.txt
index 667a862..3137e60 100644
--- a/docs/specs/ivshmem_device_spec.txt
+++ b/docs/specs/ivshmem_device_spec.txt
@@ -4,8 +4,9 @@ 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 (such as a
+hugepage) on the host. Optionally, the device may support sending interrupts
+to other guests sharing the same memory region.
Here, the new addition "such as a hugepage", in my opinion, is a bit misleading.
You may say "including hugepage-backed file" for example. Your version makes
hugepages-backed file a bit unique, it may be interpreted like only some special
files are supported, while in fact any mmap'ed file should work. And a nitpick,
it is not "hugepage", it is "hugepages".
Also, the "Optionally.." should be in the next paragraph, I think.
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index 2838866..a9f268d 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -98,6 +98,7 @@ typedef struct IVShmemState {
Error *migration_blocker;
char * shmobj;
+ char * fileobj;
char * sizearg;
char * role;
int role_val; /* scalar to avoid multiple string comparisons */
@@ -715,9 +716,9 @@ 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) {
fprintf(stderr, "WARNING: do not specify both 'chardev' "
- "and 'shm' with ivshmem\n");
+ "and 'shm' or 'file' with ivshmem\n");
Ow, this is an.. interesting wording... ;)
}
IVSHMEM_DPRINTF("using shared memory server (socket = %s)\n",
@@ -743,28 +744,42 @@ 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) {
- fprintf(stderr, "Must specify 'chardev' or 'shm' to ivshmem\n");
+ if (!(is_shm ^ is_file)) {
+ fprintf(stderr, "Must specify one, and only one, in 'chardev',"
+ " 'file' or 'shm' to ivshmem\n");
Another, even more interesting wording here ;)
Plus (tiny nitpick) an extra space before "or".
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) {
- fprintf(stderr, "ivshmem: could not truncate shared file\n");
+ 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 */
+ 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) {
+ fprintf(stderr, "ivshmem: could not truncate"
+ " shared file\n");
Here, I think, should be some exit(), even if initially there was none.
And oh, please, pretty PLEASE add some strerror(errno) reporting (again,
even if the original code had no %m reporting here). It is very sad when
users had to resort to use strace to see which error actually happens...
+ }
+
+ } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
Does it make sense to open with O_CREAT here, when previous O_EXCL
failed? It looks like we are EITHER creating a new file (above), OR
opening existing one, no?
+ S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
+ fprintf(stderr, "ivshmem: could not open shared file\n");
+ exit(-1);
}
+ } else {
+ IVSHMEM_DPRINTF("using open (file object = %s)\n", s->fileobj);
- } else if ((fd = shm_open(s->shmobj, O_CREAT|O_RDWR,
- S_IRWXU|S_IRWXG|S_IRWXO)) < 0) {
- fprintf(stderr, "ivshmem: could not open shared file\n");
- exit(-1);
-
+ /* try opening a mmap's file. This file must have been previously
+ * created on the host */
+ if ((fd = open(s->fileobj, O_RDWR)) < 0) {
+ fprintf(stderr, "ivshmem: could not open mmap'd file\n");
+ exit(-1);
+ }
}
if (check_shm_size(s, fd) == -1) {
@@ -804,6 +819,7 @@ 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(),
Can you please send a v4 with the above changes? Hopefully you agree
with them. Overall, I like this new version too.
Thank you!
/mjt
