Re: [Qemu-devel] [PATCH] qdev: Fix memory leak

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On Mon, May 14, 2012 at 09:36:36PM +0200, Stefan Weil wrote:
> Hello,
> 
> Am 03.05.2012 10:34, schrieb dunrong huang:
> >The str allocated in visit_type_str was not freed
> >
> >Signed-off-by: dunrong huang <riegamaths@gmail.com>
> >---
> >hw/qdev-properties.c | 8 ++++++--
> >1 files changed, 6 insertions(+), 2 deletions(-)
> >
> >diff --git a/hw/qdev-properties.c b/hw/qdev-properties.c
> >index 98dd06a..8088699 100644
> >--- a/hw/qdev-properties.c
> >+++ b/hw/qdev-properties.c
> >@@ -726,7 +726,7 @@ static void set_mac(Object *obj, Visitor *v,
> >void *opaque,
> >MACAddr *mac = qdev_get_prop_ptr(dev, prop);
> >Error *local_err = NULL;
> >int i, pos;
> >- char *str, *p;
> >+ char *str = NULL, *p;
> 
> Is this change really needed?
> 
> >
> >if (dev->state != DEV_STATE_CREATED) {
> >error_set(errp, QERR_PERMISSION_DENIED);
> >@@ -753,10 +753,12 @@ static void set_mac(Object *obj, Visitor *v,
> >void *opaque,
> >}
> >mac->a[i] = strtol(str+pos, &p, 16);
> >}
> >+ g_free(str);
> >return;
> >
> >inval:
> >error_set_from_qdev_prop_error(errp, EINVAL, dev, prop, str);
> >+ g_free(str);
> >}
> >
> >PropertyInfo qdev_prop_macaddr = {
> >@@ -825,7 +827,7 @@ static void set_pci_devfn(Object *obj, Visitor
> >*v, void *opaque,
> >uint32_t *ptr = qdev_get_prop_ptr(dev, prop);
> >unsigned int slot, fn, n;
> >Error *local_err = NULL;
> >- char *str = (char *)"";
> >+ char *str = NULL;
> 
> As far as I could see, str does not need an initial value, so
> neither the old nor the new code is optimal (both versions do
> work).
> 
> >
> >if (dev->state != DEV_STATE_CREATED) {
> >error_set(errp, QERR_PERMISSION_DENIED);
> >@@ -847,10 +849,12 @@ static void set_pci_devfn(Object *obj,
> >Visitor *v, void *opaque,
> >goto invalid;
> >}
> >*ptr = slot << 3 | fn;
> >+ g_free(str);
> >return;
> >
> >invalid:
> >error_set_from_qdev_prop_error(errp, EINVAL, dev, prop, str);
> >+ g_free(str);
> >}
> >
> >static int print_pci_devfn(DeviceState *dev, Property *prop, char
> >*dest, size_t len)
> 
> Maybe some expert (Michael Roth?) can comment on the correct
> usage of visit_type_str.
> 
> Is the initial value for the 2nd argument really needed?
> The current QEMU code sometimes uses initialization,
> but not always (see the code above, for example), so it is confusing.

For an output visitor (native-to-<QMP/String/etc>), we assume we're
getting a pointer to a valid string, and generally treat NULL as an indication
to generate an empty string, so the initial value matters in that case.
For that situation the changes would be warranted.

But for an input visitor (<QMP/String/etc>-to-native) like we're using in the
setters this patch modifies, the initial value gets clobbered with a pointer
to whatever the visitor allocates, so initializing the pointers isn't
neccessary.

> 
> Otherwise the patch is ok. It fixes memory leaks,
> therefore it should be added to QEMU 1.1.
> 
> Tested-by: Stefan Weil <sw@weilnetz.de>
> > Regards,
> 
> Stefan Weil
> 
>