Re: [RFT/PATCH v2] kvm tools: Add read-only support for block devices

[Ingo Molnar]

* Pekka Enberg penb...@kernel.org wrote:

 Add support for booting guests to host block devices in read-only mode.
 
 Cc: Asias He asias.he...@gmail.com
 Cc: Cyrill Gorcunov gorcu...@gmail.com
 Cc: Prasad Joshi prasadjoshi...@gmail.com
 Cc: Sasha Levin levinsasha...@gmail.com
 Cc: Ingo Molnar mi...@elte.hu
 Signed-off-by: Pekka Enberg penb...@kernel.org
 ---
  tools/kvm/disk-image.c |   39 +++
  1 files changed, 31 insertions(+), 8 deletions(-)

Nice patch - booting into the host's userspace works out of box now. The 
following disk-image-less command:

   ./kvm run ../../arch/x86/boot/bzImage --readonly --image=/dev/sda 
--params=root=/dev/vda1

has booted all the way into the host's Fedora Rawhide userspace:

   ===
   Welcome to Fedora release 16 (Rawhide)!

   [...]

   Fedora release 16 (Rawhide)
   Kernel 2.6.39-rc3-tip+ on an x86_64 (ttyS0)

   aldebaran login: 
   ===

I ran this as unprivileged user (who had read access to the partitions in 
question).

This is a very useful feature for testing kernels - i can test any random Linux 
box's userspace via KVM, without having to copy an image there! :-)

Tested-by: Ingo Molnar mi...@elte.hu

Thanks,

Ingo
--
To unsubscribe from this list: send the line unsubscribe kvm in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[RFT/PATCH v2] kvm tools: Add read-only support for block devices

[Pekka Enberg]

Add support for booting guests to host block devices in read-only mode.

Cc: Asias He asias.he...@gmail.com
Cc: Cyrill Gorcunov gorcu...@gmail.com
Cc: Prasad Joshi prasadjoshi...@gmail.com
Cc: Sasha Levin levinsasha...@gmail.com
Cc: Ingo Molnar mi...@elte.hu
Signed-off-by: Pekka Enberg penb...@kernel.org
---
 tools/kvm/disk-image.c |   39 +++
 1 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/tools/kvm/disk-image.c b/tools/kvm/disk-image.c
index fff71b4..f5e11b9 100644
--- a/tools/kvm/disk-image.c
+++ b/tools/kvm/disk-image.c
@@ -4,6 +4,9 @@
 #include kvm/qcow.h
 #include kvm/util.h
 
+#include linux/fs.h  /* for BLKGETSIZE64 */
+
+#include sys/ioctl.h
 #include sys/types.h
 #include inttypes.h
 #include sys/mman.h
@@ -110,24 +113,44 @@ static struct disk_image_operations raw_image_ro_mmap_ops 
= {
.close  = raw_image__close_sector_ro_mmap,
 };
 
-static struct disk_image *raw_image__probe(int fd, bool readonly)
+static struct disk_image *raw_image__probe(int fd, struct stat *st, bool 
readonly)
 {
-   struct stat st;
+   if (readonly)
+   return disk_image__new_readonly(fd, st-st_size, 
raw_image_ro_mmap_ops);
+   else
+   return disk_image__new(fd, st-st_size, raw_image_ops);
+}
 
-   if (fstat(fd, st)  0)
+static struct disk_image *blkdev__probe(const char *filename, struct stat *st)
+{
+   uint64_t size;
+   int fd;
+
+   if (!S_ISBLK(st-st_mode))
return NULL;
 
-   if (readonly)
-   return disk_image__new_readonly(fd, st.st_size, 
raw_image_ro_mmap_ops);
-   else
-   return disk_image__new(fd, st.st_size, raw_image_ops);
+   fd  = open(filename, O_RDONLY);
+   if (fd  0)
+   return NULL;
+
+   if (ioctl(fd, BLKGETSIZE64, size)  0)
+   return NULL;
+
+   return disk_image__new_readonly(fd, size, raw_image_ro_mmap_ops);
 }
 
 struct disk_image *disk_image__open(const char *filename, bool readonly)
 {
struct disk_image *self;
+   struct stat st;
int fd;
 
+   if (stat(filename, st)  0)
+   return NULL;
+
+   if (S_ISBLK(st.st_mode))
+   return blkdev__probe(filename, st);
+
fd  = open(filename, readonly ? O_RDONLY : O_RDWR);
if (fd  0)
return NULL;
@@ -136,7 +159,7 @@ struct disk_image *disk_image__open(const char *filename, 
bool readonly)
if (self)
return self;
 
-   self = raw_image__probe(fd, readonly);
+   self = raw_image__probe(fd, st, readonly);
if (self)
return self;
 
-- 
1.7.0.4

--
To unsubscribe from this list: send the line unsubscribe kvm in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html