[Qemu-devel] [patch]Fix block device read for some SLOW file

[Qemu-devel] [patch]Fix block device read for some SLOW file

[lepton]

Hi, I found when I am using qemu, I can't boot from emulated cdrom.
After some debug, I found the reason is that my iso file is in a samba
file system. When qemu read data from my samba file system. read will be
interrupted by signal alarm. So qemu won't boot from it.

The follwing patch will fix it.

--- qemu-0.7.1/block.c	2005-07-25 02:52:08.000000000 +0800
+++ qemu-0.7.1-lepton/block.c	2005-07-27 18:57:21.000000000 +0800
@@ -591,10 +591,16 @@ static int raw_read(BlockDriverState *bs
     int ret;
     
     lseek(s->fd, sector_num * 512, SEEK_SET);
-    ret = read(s->fd, buf, nb_sectors * 512);
-    if (ret != nb_sectors * 512) 
-        return -1;
-    return 0;
+    while(1){
+  	ret = read(s->fd, buf, nb_sectors * 512);
+	if (ret != nb_sectors * 512) {
+		if(ret==-1 && errno==EINTR)
+			continue;
+	    	else
+        		return -1;
+	}
+	return 0;
+    }
 }
 
 static int raw_write(BlockDriverState *bs, int64_t sector_num, 

Re: [Qemu-devel] [patch]Fix block device read for some SLOW file

[Johannes Schindelin]

Hi,

On Wed, 27 Jul 2005, lepton wrote:

> +    while(1){
> +  	ret = read(s->fd, buf, nb_sectors * 512);
> +	if (ret != nb_sectors * 512) {
> +		if(ret==-1 && errno==EINTR)
> +			continue;
> +	    	else
> +        		return -1;
> +	}
> +	return 0;
> +    }

Why not

do {
	ret = read(s->fd, buf, nb_sectors * 512);
} while(ret==-1 && errno=EINTR);

if (ret != nb_sectors * 512)
	return -1;
return 0;

Ciao,
Dscho

[Qemu-devel] Re: [patch]Fix block device read for some SLOW file

[Jani Monoses]

lepton wrote:
> Hi, I found when I am using qemu, I can't boot from emulated cdrom.
> After some debug, I found the reason is that my iso file is in a samba
> file system. When qemu read data from my samba file system. read will be
> interrupted by signal alarm. So qemu won't boot from it.
> 
> The follwing patch will fix it.
> 
> --- qemu-0.7.1/block.c	2005-07-25 02:52:08.000000000 +0800
> +++ qemu-0.7.1-lepton/block.c	2005-07-27 18:57:21.000000000 +0800
> @@ -591,10 +591,16 @@ static int raw_read(BlockDriverState *bs
>      int ret;
>      
>      lseek(s->fd, sector_num * 512, SEEK_SET);
> -    ret = read(s->fd, buf, nb_sectors * 512);
> -    if (ret != nb_sectors * 512) 
> -        return -1;
> -    return 0;

There's another error related to this code: qemu won't boot floppy images whose size isn't 
a multiple of 512, it will drop the last incomplete sector, as the last read will not give 
512 bytes.
a good testcase is the asmutils linux floppy image.

Jani