This option complements -mem-path. It implies -mem-prealloc. If specified,
the guest RAM is allocated as a shared memory object. If both -mem-path
and -mem-share are provided, the memory is allocated from the HugeTLBFS
supplied path, and then mmapped with MAP_SHARED.
Signed-off-by: Antonios Motakis <a.mota...@virtualopensystems.com>
Signed-off-by: Nikolay Nikolaev <n.nikol...@virtualopensystems.com>
---
exec.c | 72 +++++++++++++++++++++++++++++++++++---------------
include/exec/cpu-all.h | 1 +
qemu-options.hx | 9 +++++++
vl.c | 5 ++++
4 files changed, 66 insertions(+), 21 deletions(-)
diff --git a/exec.c b/exec.c
index f4b9ef2..10720f1 100644
--- a/exec.c
+++ b/exec.c
@@ -883,6 +883,7 @@ void qemu_mutex_unlock_ramlist(void)
#include <sys/vfs.h>
#define HUGETLBFS_MAGIC 0x958458f6
+#define MIN_HUGE_PAGE_SIZE (2*1024*1024)
static long gethugepagesize(const char *path)
{
@@ -920,15 +921,24 @@ static void *file_ram_alloc(RAMBlock *block,
char *c;
void *area;
int fd;
+ int flags;
unsigned long hpagesize;
- hpagesize = gethugepagesize(path);
- if (!hpagesize) {
- return NULL;
- }
+ if (path) {
+ hpagesize = gethugepagesize(path);
- if (memory < hpagesize) {
- return NULL;
+ if (!hpagesize) {
+ return NULL ;
+ }
+
+ if (memory < hpagesize) {
+ return NULL ;
+ }
+ } else {
+ if (memory < MIN_HUGE_PAGE_SIZE) {
+ return NULL ;
+ }
+ hpagesize = MIN_HUGE_PAGE_SIZE;
}
if (kvm_enabled() && !kvm_has_sync_mmu()) {
@@ -943,20 +953,37 @@ static void *file_ram_alloc(RAMBlock *block,
*c = '_';
}
- filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
- sanitized_name);
- g_free(sanitized_name);
+ if (path) {
+
+ filename = g_strdup_printf("%s/qemu_back_mem.%s.XXXXXX", path,
+ sanitized_name);
+ g_free(sanitized_name);
- fd = mkstemp(filename);
- if (fd < 0) {
- perror("unable to create backing store for hugepages");
+ fd = mkstemp(filename);
+ if (fd < 0) {
+ perror("unable to create backing store for huge");
+ g_free(filename);
+ return NULL ;
+ }
+ unlink(filename);
g_free(filename);
+ memory = (memory + hpagesize - 1) & ~(hpagesize - 1);
+ } else if (mem_share) {
+ filename = g_strdup_printf("qemu_back_mem.%s.XXXXXX", sanitized_name);
+ g_free(sanitized_name);
+ fd = shm_open(filename, O_CREAT | O_RDWR | O_EXCL,
+ S_IRWXU | S_IRWXG | S_IRWXO);
+ if (fd < 0) {
+ perror("unable to create backing store for shared memory");
+ g_free(filename);
+ return NULL ;
+ }
+ shm_unlink(filename);
+ g_free(filename);
+ } else {
+ fprintf(stderr, "-mem-path or -mem-share required\n");
return NULL;
}
- unlink(filename);
- g_free(filename);
-
- memory = (memory+hpagesize-1) & ~(hpagesize-1);
/*
* ftruncate is not supported by hugetlbfs in older
@@ -967,7 +994,8 @@ static void *file_ram_alloc(RAMBlock *block,
if (ftruncate(fd, memory))
perror("ftruncate");
- area = mmap(0, memory, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+ flags = mem_share ? MAP_SHARED : MAP_PRIVATE;
+ area = mmap(0, memory, PROT_READ | PROT_WRITE, flags, fd, 0);
if (area == MAP_FAILED) {
perror("file_ram_alloc: can't mmap RAM pages");
close(fd);
@@ -1150,13 +1178,14 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size,
void *host,
new_block->host = host;
new_block->flags |= RAM_PREALLOC_MASK;
} else if (xen_enabled()) {
- if (mem_path) {
- fprintf(stderr, "-mem-path not supported with Xen\n");
+ if (mem_path || mem_share) {
+ fprintf(stderr,
+ "-mem-path and -mem-share not supported with Xen\n");
exit(1);
}
xen_ram_alloc(new_block->offset, size, mr);
} else {
- if (mem_path) {
+ if (mem_path || mem_share) {
if (phys_mem_alloc != qemu_anon_ram_alloc) {
/*
* file_ram_alloc() needs to allocate just like
@@ -1164,7 +1193,8 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void
*host,
* a hook there.
*/
fprintf(stderr,
- "-mem-path not supported with this accelerator\n");
+ "-mem-path and -mem-share "
+ "not supported with this accelerator\n");
exit(1);
}
new_block->host = file_ram_alloc(new_block, size, mem_path);
diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index b6998f0..05ad0ee 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -469,6 +469,7 @@ extern RAMList ram_list;
extern const char *mem_path;
extern int mem_prealloc;
+extern int mem_share;
/* Flags stored in the low bits of the TLB virtual address. These are
defined so that fast path ram access is all zeros. */
diff --git a/qemu-options.hx b/qemu-options.hx
index af34483..bd70777 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -237,6 +237,15 @@ STEXI
Preallocate memory when using -mem-path.
ETEXI
+DEF("mem-share", 0, QEMU_OPTION_mem_share,
+ "-mem-share share guest memory (implies -mem-prealloc)\n",
+ QEMU_ARCH_ALL)
+STEXI
+@item -mem-share
+@findex -mem-share
+Allocate guest RAM as a shared memory object.
+ETEXI
+
DEF("k", HAS_ARG, QEMU_OPTION_k,
"-k language use keyboard layout (for example 'fr' for French)\n",
QEMU_ARCH_ALL)
diff --git a/vl.c b/vl.c
index b0399de..d2f7403 100644
--- a/vl.c
+++ b/vl.c
@@ -189,6 +189,7 @@ const char* keyboard_layout = NULL;
ram_addr_t ram_size;
const char *mem_path = NULL;
int mem_prealloc = 0; /* force preallocation of physical target memory */
+int mem_share = 0; /* allocate shared memory */
int nb_nics;
NICInfo nd_table[MAX_NICS];
int autostart;
@@ -3212,6 +3213,10 @@ int main(int argc, char **argv, char **envp)
case QEMU_OPTION_mem_prealloc:
mem_prealloc = 1;
break;
+ case QEMU_OPTION_mem_share:
+ mem_share = 1;
+ mem_prealloc = 1;
+ break;
case QEMU_OPTION_d:
log_mask = optarg;
break;
--
1.8.3.2
