On 10/31/2015 09:45 PM, Eduardo Habkost wrote:
On Sat, Oct 31, 2015 at 04:46:05PM +0800, Xiao Guangrong wrote:
On 10/31/2015 01:30 AM, Eduardo Habkost wrote:
On Fri, Oct 30, 2015 at 01:56:05PM +0800, Xiao Guangrong wrote:
Use the whole file size if @size is not specified which is useful
if we want to directly pass a file to guest

Signed-off-by: Xiao Guangrong <guangrong.x...@linux.intel.com>
  backends/hostmem-file.c | 48 ++++++++++++++++++++++++++++++++++++++++++++----
  1 file changed, 44 insertions(+), 4 deletions(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 9097a57..e1bc9ff 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -9,6 +9,9 @@
   * This work is licensed under the terms of the GNU GPL, version 2 or later.
   * See the COPYING file in the top-level directory.
+#include <sys/ioctl.h>
+#include <linux/fs.h>

This code needs to build on other platforms too. e.g. using mingw32:

Err... You did it on Windows? It's surprised that the file is only built
on Linux:
common-obj-$(CONFIG_LINUX) += hostmem-file.o

How it can happen...

I did it using mingw32. I don't remember what I did, but I probably tried
something stupid to test just the build of hostmem-file.o and didn't notice it
was conditional on CONFIG_LINUX. Sorry for the noise.

No problem. :)

   CC    backends/hostmem-file.o
/home/ehabkost/rh/proj/virt/qemu/backends/hostmem-file.c:12:23: fatal error: 
sys/ioctl.h: No such file or directory
  #include <sys/ioctl.h>
compilation terminated.
/home/ehabkost/rh/proj/virt/qemu/rules.mak:57: recipe for target 
'backends/hostmem-file.o' failed
make: *** [backends/hostmem-file.o] Error 1

  #include "qemu-common.h"
  #include "sysemu/hostmem.h"
  #include "sysemu/sysemu.h"
@@ -33,20 +36,57 @@ struct HostMemoryBackendFile {
      char *mem_path;

+static uint64_t get_file_size(const char *file)
+    struct stat stat_buf;
+    uint64_t size = 0;
+    int fd;
+    fd = open(file, O_RDONLY);
+    if (fd < 0) {
+        return 0;
+    }
+    if (stat(file, &stat_buf) < 0) {
+        goto exit;
+    }
+    if ((S_ISBLK(stat_buf.st_mode)) && !ioctl(fd, BLKGETSIZE64, &size)) {
+        goto exit;
+    }

I have another question: if our block device code at raw-posix.c doesn't need
the Linux-specific BLKGETSIZE64 call, why exactly do we need it in
hostmem-file.c? In which cases it would break without BLKGETSIZE64?

I guess the function at raw-posix.c did not realize it will work
on raw block device directly.

+    size = lseek(fd, 0, SEEK_END);
+    if (size == -1) {
+        size = 0;
+    }
+    close(fd);
+    return size;

This code seems to duplicate what block/raw-posix.c:raw_getlength() does
(except for the BLKGETSIZE64 part). Have you considered using the same
code for both?

We can probably move all the raw-posix.c raw_getlength(BlockDriverState
*bs) code to fd_getlength(int fd) functions (on osdep.c?), and just
implement raw-posix.c:raw_getlength(s) as fd_getlength(s->fd).

Actually, Paolo has the same suggestion before... but

| The function you pointed out is really complex - it mixed 9 platforms and each
| platform has its own specific implementation. It is hard for us to verify the
| change.
| I'd prefer to make it for Linux specific first then share it to other 
| if it's needed in the future.

I do not know if it's really worth doing it. :(

If hostmem-file.c is Linux-specific we don't need to move or reuse the code for
all the other 9 platforms right now, that's true. But now you are adding a new
arch-specific function that does exactly the same thing in a different file to
the mix. What if somebody want to make hostmem-file.c work in another platform
in the future, and begin to duplicate the same #ifdef mess from raw-posix.c?

I was considering this:

1) Move the arch-independent raw_getlength() code to fd_getlength() (at
osdep.c, maybe?), as:

int64_t fd_getlength(int fd)
     int64_t size;

     size = lseek(s->fd, 0, SEEK_END);
     if (size < 0) {
         return -errno;
     return size;

2) Change the arch-independent version of raw_getlength() to:

static int64_t raw_getlength(BlockDriverState *bs)
     BDRVRawState *s = bs->opaque;
     int ret;
     int64_t size;

     ret = fd_open(bs);
     if (ret < 0) {
         return ret;

     return fd_getlength(s->fd);

3) Implement get_file_size() using fd_getlength():

uint64_t get_file_size(const char *file, Error **errp)
     struct stat stat_buf;
     int64_t size = 0;
     int fd;

     fd = open(file, O_RDONLY);
     if (fd < 0) {
         error_setg_errno(errp, errno, "can't open file %s", file);
         return 0;

     size = fd_getlength(fd);
     if (size < 0) {
         error_setg_errno(errp, -size, "can't get size of file %s", file);
         size = 0;

     return size;

4) In case BLKGETSIZE64 is really necesary, add a Linux-specific block to

int64_t fd_getlength(int fd)
     int64_t size;

     struct stat stat_buf;
     if (fstat(fd, &stat_buf) < 0) {
         return -errno;

     if ((S_ISBLK(stat_buf.st_mode)) && !ioctl(fd, BLKGETSIZE64, &size)) {
         if (size < 0) {
             return -EOVERFLOW;
         return size;

     size = lseek(fd, 0, SEEK_END);
     if (size < 0) {
         return -errno;

     return size;

People working on other platforms will be able to move arch-specific code to
fd_getlength() later, if they want to.

Fair enough to me and really smart. Will do it in next version.

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