Patchwork [v4,2/3] Support adding a file to qemu's ram allocation

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Submitter Cam Macdonell
Date April 7, 2010, 10:51 p.m.
Message ID <1270680720-8457-3-git-send-email-cam@cs.ualberta.ca>
Download mbox | patch
Permalink /patch/49670/
State New
Headers show

Comments

Cam Macdonell - April 7, 2010, 10:51 p.m.
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(-)
Avi Kivity - April 12, 2010, 8:38 p.m.
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.

Patch

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;