Re: [PATCH v4 2/3] Support adding a file to qemu's ram allocation

[Avi Kivity]

On 04/08/2010 01:51 AM, Cam Macdonell wrote:

This avoids the need of using qemu_ram_alloc and mmap with MAP_FIXED to map a
host file into guest RAM.  This function mmaps the opened file anywhere and adds
the memory to the ram blocks.

Usage is

qemu_ram_mmap(fd, size, MAP_SHARED, offset);
---
  cpu-common.h |1 +
  exec.c   |   33 +
  2 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/cpu-common.h b/cpu-common.h
index 49c7fb3..87c82fc 100644
--- a/cpu-common.h
+++ b/cpu-common.h
@@ -32,6 +32,7 @@ static inline void 
cpu_register_physical_memory(target_phys_addr_t start_addr,
  }

  ram_addr_t cpu_get_physical_page_desc(target_phys_addr_t addr);
+ram_addr_t qemu_ram_mmap(int, ram_addr_t, int, int);
   


Use prototypes with argument names please.  That's not the style around 
it, but that's bad style.




+ram_addr_t qemu_ram_mmap(int fd, ram_addr_t size, int flags, int offset)
   


off_t offset


+{
+RAMBlock *new_block;
+
+size = TARGET_PAGE_ALIGN(size);
+new_block = qemu_malloc(sizeof(*new_block));
+
+// map the file passed as a parameter to be this part of memory
   


/* comments */


+new_block->host = mmap(0, size, PROT_READ|PROT_WRITE, flags, fd, offset);
   


Error checking.


+
+#ifdef MADV_MERGEABLE
+madvise(new_block->host, size, MADV_MERGEABLE);
+#endif
   


Won't work (ksm only merges anonymous pages), but keep it there in case 
it learns about pagecache.



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Do not meddle in the internals of kernels, for they are subtle and quick to 
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[PATCH v4 2/3] Support adding a file to qemu's ram allocation

[Cam Macdonell]

This avoids the need of using qemu_ram_alloc and mmap with MAP_FIXED to map a
host file into guest RAM.  This function mmaps the opened file anywhere and adds
the memory to the ram blocks.

Usage is

qemu_ram_mmap(fd, size, MAP_SHARED, offset);
---
 cpu-common.h |1 +
 exec.c   |   33 +
 2 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/cpu-common.h b/cpu-common.h
index 49c7fb3..87c82fc 100644
--- a/cpu-common.h
+++ b/cpu-common.h
@@ -32,6 +32,7 @@ static inline void 
cpu_register_physical_memory(target_phys_addr_t start_addr,
 }
 
 ram_addr_t cpu_get_physical_page_desc(target_phys_addr_t addr);
+ram_addr_t qemu_ram_mmap(int, ram_addr_t, int, int);
 ram_addr_t qemu_ram_alloc(ram_addr_t);
 void qemu_ram_free(ram_addr_t addr);
 /* This should only be used for ram local to a device.  */
diff --git a/exec.c b/exec.c
index 467a0e7..2303be7 100644
--- a/exec.c
+++ b/exec.c
@@ -2811,6 +2811,39 @@ static void *file_ram_alloc(ram_addr_t memory, const 
char *path)
 }
 #endif
 
+ram_addr_t qemu_ram_mmap(int fd, ram_addr_t size, int flags, int offset)
+{
+RAMBlock *new_block;
+
+size = TARGET_PAGE_ALIGN(size);
+new_block = qemu_malloc(sizeof(*new_block));
+
+// map the file passed as a parameter to be this part of memory
+new_block->host = mmap(0, size, PROT_READ|PROT_WRITE, flags, fd, offset);
+
+#ifdef MADV_MERGEABLE
+madvise(new_block->host, size, MADV_MERGEABLE);
+#endif
+
+new_block->offset = last_ram_offset;
+new_block->length = size;
+
+new_block->next = ram_blocks;
+ram_blocks = new_block;
+
+phys_ram_dirty = qemu_realloc(phys_ram_dirty,
+(last_ram_offset + size) >> TARGET_PAGE_BITS);
+memset(phys_ram_dirty + (last_ram_offset >> TARGET_PAGE_BITS),
+   0xff, size >> TARGET_PAGE_BITS);
+
+last_ram_offset += size;
+
+if (kvm_enabled())
+kvm_setup_guest_memory(new_block->host, size);
+
+return new_block->offset;
+}
+
 ram_addr_t qemu_ram_alloc(ram_addr_t size)
 {
 RAMBlock *new_block;
-- 
1.6.0.6

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