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

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 [off-list ref] wrote:

Hi,

quoted

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 <redacted>
---
 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.

quoted

 
 __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.

quoted

+	} 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.

quoted

+	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

quoted

+
+	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",

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