Re: [PATCH v3 kvmtool 09/13] builtin_run: Allow standard size specifiers for memory

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

Thank you for having a look! Replies below.

On Wed, Jun 01, 2022 at 02:39:55PM +0100, Andre Przywara wrote:
> On Wed, 25 May 2022 12:23:41 +0100
> Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> Hi,
> 
> > From: Suzuki K Poulose <suzuki.poulose@arm.com>
> > 
> > Allow the user to use the standard B (bytes), K (kilobytes), M (megabytes),
> > G (gigabytes), T (terabytes) and P (petabytes) suffixes for memory size.
> > When none are specified, the default is megabytes.
> > 
> > Also raise an error if the guest specifies 0 as the memory size, instead
> > of treating it as uninitialized, as kvmtool has done so far.
> > 
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> > ---
> >  builtin-run.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 60 insertions(+), 5 deletions(-)
> > 
> > diff --git a/builtin-run.c b/builtin-run.c
> > index 2ef159cdb2a3..a49698d5b2fe 100644
> > --- a/builtin-run.c
> > +++ b/builtin-run.c
> > @@ -49,9 +49,11 @@
> >  #include <ctype.h>
> >  #include <stdio.h>
> >  
> > -#define MB_SHIFT		(20)
> >  #define KB_SHIFT		(10)
> > +#define MB_SHIFT		(20)
> >  #define GB_SHIFT		(30)
> > +#define TB_SHIFT		(40)
> > +#define PB_SHIFT		(50)
> 
> Can we lose the parentheses?

Yes.

> 
> >  
> >  __thread struct kvm_cpu *current_kvm_cpu;
> >  
> > @@ -87,6 +89,60 @@ void kvm_run_set_wrapper_sandbox(void)
> >  	kvm_run_wrapper = KVM_RUN_SANDBOX;
> >  }
> >  
> > +static int parse_mem_unit(char **next)
> > +{
> > +	int shift = -1;
> > +
> > +	switch (**next) {
> > +	case 'B': case 'b': shift = 0; break;
> > +	case 'K': case 'k': shift = KB_SHIFT; break;
> > +	case 'M': case 'm': shift = MB_SHIFT; break;
> > +	case 'G': case 'g': shift = GB_SHIFT; break;
> > +	case 'T': case 't': shift = TB_SHIFT; break;
> > +	case 'P': case 'p': shift = PB_SHIFT; break;
> > +	}
> > +
> > +	if (shift == -1) {
> > +		/* The default is megabytes. */
> > +		shift = MB_SHIFT;
> 
> Doesn't that look better inside the switch/case?
> 	default: return MB_SHIFT;

I think that change alone breaks the logic.

The code needs to advance next if and only if it matches on one of the
characters. I'll have a go at advancing next in each of the switch arms
above (with the exception of the default one, which I'll add) to see how it
ends up looking.

> 
> > +	} else {
> > +		(*next)++;
> > +	}
> > +
> > +	return shift;
> > +}
> > +
> > +static u64 parse_mem_option(const char *nptr, char **next)
> > +{
> > +	u64 shift;
> > +	u64 val;
> > +
> > +	val = strtoull(nptr, next, 10);
> > +	if (errno == ERANGE)
> > +		die("Memory too large: %s", nptr);
> 
> strtoull does not clear errno if it succeeds, so it retains the
> previous error value. So we would need to set errno to 0 just before
> calling strtoull.

This was intentional on my part, because I was under the impression that
kvmtool treats all instances where errno != 0 as a fatal error. I think I
was wrong about that, I see at least one instance when that isn't the case,
in kvm_setup_guest_init -> extract_file. So it isn't a rule that a non-zero
errno is a fatal error.

I'll change the code to zero errno before calling strtoull.

> 
> > +	shift = parse_mem_unit(next);
> > +
> > +	if ((val << shift) < val)
> > +		die("Memory too large: %s", nptr);
> > +
> > +	return val << shift;
> > +}
> > +
> > +static int mem_parser(const struct option *opt, const char *arg, int unset)
> > +{
> > +	struct kvm *kvm = opt->ptr;
> > +	char *next;
> > +
> > +	kvm->cfg.ram_size = parse_mem_option(arg, &next);
> > +	if (kvm->cfg.ram_size == 0)
> > +		die("Invalid RAM size: %s", arg);
> 
> Does 0 hold any significant value (anymore)? I think we die() if we
> encounter invalid values in parse_mem_option()?

strtoull does not consider an error to convert the string "0" to an
unsigned long long.

Thanks,
Alex

> 
> Cheers,
> Andre
> 
> > +
> > +	if (*next != '\0')
> > +		die("Invalid memory specifier: %s", arg);
> > +
> > +	return 0;
> > +}
> > +
> >  #ifndef OPT_ARCH_RUN
> >  #define OPT_ARCH_RUN(...)
> >  #endif
> > @@ -97,8 +153,9 @@ void kvm_run_set_wrapper_sandbox(void)
> >  	OPT_STRING('\0', "name", &(cfg)->guest_name, "guest name",	\
> >  			"A name for the guest"),			\
> >  	OPT_INTEGER('c', "cpus", &(cfg)->nrcpus, "Number of CPUs"),	\
> > -	OPT_U64('m', "mem", &(cfg)->ram_size, "Virtual machine memory"	\
> > -		" size in MB."),					\
> > +	OPT_CALLBACK('m', "mem", NULL, "size[BKMGTP]",			\
> > +		     "Virtual machine memory size, by default measured"	\
> > +		     " in megabytes (M)", mem_parser, kvm),		\
> >  	OPT_CALLBACK('d', "disk", kvm, "image or rootfs_dir", "Disk "	\
> >  			" image or rootfs directory", img_name_parser,	\
> >  			kvm),						\
> > @@ -522,8 +579,6 @@ static void kvm_run_validate_cfg(struct kvm *kvm)
> >  		pr_warning("Ignoring initrd file when loading a firmware image");
> >  
> >  	if (kvm->cfg.ram_size) {
> > -		/* User specifies RAM size in megabytes. */
> > -		kvm->cfg.ram_size <<= MB_SHIFT;
> >  		available_ram = host_ram_size();
> >  		if (available_ram && kvm->cfg.ram_size > available_ram) {
> >  			pr_warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB",
> 

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel