[PATCH v2] tests/9pfs: Use g_autofree and g_autoptr where possible

[PATCH v2] tests/9pfs: Use g_autofree and g_autoptr where possible

[Greg Kurz]

It is recommended to use g_autofree or g_autoptr as it reduces
the odds of introducing memory leaks in future changes. Let's do
that everywhere a glib allocation is performed.

The virtio_9p_create_local_test_dir() function needs some extra
care though : the template pointer is eventually cached into the
local_test_path global variable for the duration of the tests and
should not be freed. Add the g_autofree annotation but negate it
with g_steal_pointer() to make it clear that the pointer ownership
is dropped on purpose.

Based-on: <f6602123c6f7d0d593466231b04fba087817abbd.1642879848.git.qemu_oss@crudebyte.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
---
v2: - fix crash with local_test_path
---
 tests/qtest/libqos/virtio-9p.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/tests/qtest/libqos/virtio-9p.c b/tests/qtest/libqos/virtio-9p.c
index ef96ef006adc..f0ffbc583492 100644
--- a/tests/qtest/libqos/virtio-9p.c
+++ b/tests/qtest/libqos/virtio-9p.c
@@ -37,18 +37,22 @@ static char *concat_path(const char* a, const char* b)
     return g_build_filename(a, b, NULL);
 }
 
-void virtio_9p_create_local_test_dir(void)
+static char *make_temp_dir(char *template)
 {
-    struct stat st;
-    char *pwd = g_get_current_dir();
-    char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
-
-    local_test_path = mkdtemp(template);
-    if (!local_test_path) {
+    char *path = mkdtemp(template);
+    if (!path) {
         g_test_message("mkdtemp('%s') failed: %s", template, strerror(errno));
     }
-    g_free(pwd);
+    return path;
+}
+
+void virtio_9p_create_local_test_dir(void)
+{
+    g_autofree char *pwd = g_get_current_dir();
+    g_autofree char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
+    struct stat st;
 
+    local_test_path = make_temp_dir(g_steal_pointer(&template));
     g_assert(local_test_path != NULL);
 
     /* ensure test directory exists now ... */
@@ -60,12 +64,11 @@ void virtio_9p_create_local_test_dir(void)
 void virtio_9p_remove_local_test_dir(void)
 {
     g_assert(local_test_path != NULL);
-    char *cmd = g_strdup_printf("rm -fr '%s'\n", local_test_path);
+    g_autofree char *cmd = g_strdup_printf("rm -fr '%s'\n", local_test_path);
     int res = system(cmd);
     if (res < 0) {
         /* ignore error, dummy check to prevent compiler error */
     }
-    g_free(cmd);
 }
 
 char *virtio_9p_test_path(const char *path)
@@ -209,8 +212,8 @@ static void *virtio_9p_pci_create(void *pci_bus, QGuestAllocator *t_alloc,
 static void regex_replace(GString *haystack, const char *pattern,
                           const char *replace_fmt, ...)
 {
-    GRegex *regex;
-    char *replace, *s;
+    g_autoptr(GRegex) regex = NULL;
+    g_autofree char *replace = NULL, *s = NULL;
     va_list argp;
 
     va_start(argp, replace_fmt);
@@ -220,9 +223,6 @@ static void regex_replace(GString *haystack, const char *pattern,
     regex = g_regex_new(pattern, 0, 0, NULL);
     s = g_regex_replace(regex, haystack->str, -1, 0, replace, 0, NULL);
     g_string_assign(haystack, s);
-    g_free(s);
-    g_regex_unref(regex);
-    g_free(replace);
 }
 
 void virtio_9p_assign_local_driver(GString *cmd_line, const char *args)
-- 
2.34.1

Re: [PATCH v2] tests/9pfs: Use g_autofree and g_autoptr where possible

[Christian Schoenebeck]

On Montag, 31. Januar 2022 17:39:30 CET Greg Kurz wrote:
> It is recommended to use g_autofree or g_autoptr as it reduces
> the odds of introducing memory leaks in future changes. Let's do
> that everywhere a glib allocation is performed.
> 
> The virtio_9p_create_local_test_dir() function needs some extra
> care though : the template pointer is eventually cached into the
> local_test_path global variable for the duration of the tests and
> should not be freed. Add the g_autofree annotation but negate it
> with g_steal_pointer() to make it clear that the pointer ownership
> is dropped on purpose.
> 
> Based-on:
> <f6602123c6f7d0d593466231b04fba087817abbd.1642879848.git.qemu_oss@crudebyte
> .com> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v2: - fix crash with local_test_path
> ---
>  tests/qtest/libqos/virtio-9p.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/tests/qtest/libqos/virtio-9p.c b/tests/qtest/libqos/virtio-9p.c
> index ef96ef006adc..f0ffbc583492 100644
> --- a/tests/qtest/libqos/virtio-9p.c
> +++ b/tests/qtest/libqos/virtio-9p.c
> @@ -37,18 +37,22 @@ static char *concat_path(const char* a, const char* b)
>      return g_build_filename(a, b, NULL);
>  }
> 
> -void virtio_9p_create_local_test_dir(void)
> +static char *make_temp_dir(char *template)
>  {
> -    struct stat st;
> -    char *pwd = g_get_current_dir();
> -    char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
> -
> -    local_test_path = mkdtemp(template);
> -    if (!local_test_path) {
> +    char *path = mkdtemp(template);
> +    if (!path) {
>          g_test_message("mkdtemp('%s') failed: %s", template,
> strerror(errno)); }
> -    g_free(pwd);
> +    return path;
> +}
> +
> +void virtio_9p_create_local_test_dir(void)
> +{
> +    g_autofree char *pwd = g_get_current_dir();
> +    g_autofree char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
> +    struct stat st;
> 
> +    local_test_path = make_temp_dir(g_steal_pointer(&template));

Quite noisy diff and under the bottom line, it does not fix what it originally 
supposed to: addressing the leak of the global variable 'local_test_path'. 
g_steal_pointer() simply makes the previous g_autofree prefix pointless.

Why not just moving g_autofree from 'template' to the global variable 
'local_test_path' and avoid all that noise? 

>      g_assert(local_test_path != NULL);
> 
>      /* ensure test directory exists now ... */
> @@ -60,12 +64,11 @@ void virtio_9p_create_local_test_dir(void)
>  void virtio_9p_remove_local_test_dir(void)
>  {
>      g_assert(local_test_path != NULL);
> -    char *cmd = g_strdup_printf("rm -fr '%s'\n", local_test_path);
> +    g_autofree char *cmd = g_strdup_printf("rm -fr '%s'\n",
> local_test_path); int res = system(cmd);
>      if (res < 0) {
>          /* ignore error, dummy check to prevent compiler error */
>      }
> -    g_free(cmd);
>  }
> 
>  char *virtio_9p_test_path(const char *path)
> @@ -209,8 +212,8 @@ static void *virtio_9p_pci_create(void *pci_bus,
> QGuestAllocator *t_alloc, static void regex_replace(GString *haystack,
> const char *pattern, const char *replace_fmt, ...)
>  {
> -    GRegex *regex;
> -    char *replace, *s;
> +    g_autoptr(GRegex) regex = NULL;
> +    g_autofree char *replace = NULL, *s = NULL;
>      va_list argp;
> 
>      va_start(argp, replace_fmt);
> @@ -220,9 +223,6 @@ static void regex_replace(GString *haystack, const char
> *pattern, regex = g_regex_new(pattern, 0, 0, NULL);
>      s = g_regex_replace(regex, haystack->str, -1, 0, replace, 0, NULL);
>      g_string_assign(haystack, s);
> -    g_free(s);
> -    g_regex_unref(regex);
> -    g_free(replace);
>  }
> 
>  void virtio_9p_assign_local_driver(GString *cmd_line, const char *args)

Re: [PATCH v2] tests/9pfs: Use g_autofree and g_autoptr where possible

[Greg Kurz]

On Mon, 31 Jan 2022 18:43:22 +0100
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> On Montag, 31. Januar 2022 17:39:30 CET Greg Kurz wrote:
> > It is recommended to use g_autofree or g_autoptr as it reduces
> > the odds of introducing memory leaks in future changes. Let's do
> > that everywhere a glib allocation is performed.
> > 
> > The virtio_9p_create_local_test_dir() function needs some extra
> > care though : the template pointer is eventually cached into the
> > local_test_path global variable for the duration of the tests and
> > should not be freed. Add the g_autofree annotation but negate it
> > with g_steal_pointer() to make it clear that the pointer ownership
> > is dropped on purpose.
> > 
> > Based-on:
> > <f6602123c6f7d0d593466231b04fba087817abbd.1642879848.git.qemu_oss@crudebyte
> > .com> Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> > v2: - fix crash with local_test_path
> > ---
> >  tests/qtest/libqos/virtio-9p.c | 30 +++++++++++++++---------------
> >  1 file changed, 15 insertions(+), 15 deletions(-)
> > 
> > diff --git a/tests/qtest/libqos/virtio-9p.c b/tests/qtest/libqos/virtio-9p.c
> > index ef96ef006adc..f0ffbc583492 100644
> > --- a/tests/qtest/libqos/virtio-9p.c
> > +++ b/tests/qtest/libqos/virtio-9p.c
> > @@ -37,18 +37,22 @@ static char *concat_path(const char* a, const char* b)
> >      return g_build_filename(a, b, NULL);
> >  }
> > 
> > -void virtio_9p_create_local_test_dir(void)
> > +static char *make_temp_dir(char *template)
> >  {
> > -    struct stat st;
> > -    char *pwd = g_get_current_dir();
> > -    char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
> > -
> > -    local_test_path = mkdtemp(template);
> > -    if (!local_test_path) {
> > +    char *path = mkdtemp(template);
> > +    if (!path) {
> >          g_test_message("mkdtemp('%s') failed: %s", template,
> > strerror(errno)); }
> > -    g_free(pwd);
> > +    return path;
> > +}
> > +
> > +void virtio_9p_create_local_test_dir(void)
> > +{
> > +    g_autofree char *pwd = g_get_current_dir();
> > +    g_autofree char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
> > +    struct stat st;
> > 
> > +    local_test_path = make_temp_dir(g_steal_pointer(&template));
> 
> Quite noisy diff and under the bottom line, it does not fix what it originally 
> supposed to: addressing the leak of the global variable 'local_test_path'. 
> g_steal_pointer() simply makes the previous g_autofree prefix pointless.
> 

The g_autofree and g_steal_pointer() dance is just an idiom that
says "I'm not freeing this pointer on purpose, it will be handled
somewhere else". No big deal. I'll split this in two patches : one
for the leak of 'local_test_path' with a clear comment instead of
g_autofree and one for the remaining g_auto* conversions.

> Why not just moving g_autofree from 'template' to the global variable 
> 'local_test_path' and avoid all that noise? 
> 

Because the 'cleanup' attribute cannot be set on a static variable as
documented in GCC:

cleanup (cleanup_function)

    The cleanup attribute runs a function when the variable goes out of
    scope. This attribute can only be applied to auto function scope
    variables; it may not be applied to parameters or variables with
    static storage duration. The function must take one parameter, a
    pointer to a type compatible with the variable. The return value
    of the function (if any) is ignored. 

and trying to do so produces:

../../tests/qtest/libqos/virtio-9p.c:32:1: error: ‘cleanup’ attribute ignored [-Werror=attributes]
   32 | static g_autofree char *local_test_path;
      | ^~~~~~
cc1: all warnings being treated as errors

The leak of 'local_test_path' can only be addressed with a g_free()
in its last user, i.e. virtio_9p_remove_local_test_dir().

> >      g_assert(local_test_path != NULL);
> > 
> >      /* ensure test directory exists now ... */
> > @@ -60,12 +64,11 @@ void virtio_9p_create_local_test_dir(void)
> >  void virtio_9p_remove_local_test_dir(void)
> >  {
> >      g_assert(local_test_path != NULL);
> > -    char *cmd = g_strdup_printf("rm -fr '%s'\n", local_test_path);
> > +    g_autofree char *cmd = g_strdup_printf("rm -fr '%s'\n",
> > local_test_path); int res = system(cmd);
> >      if (res < 0) {
> >          /* ignore error, dummy check to prevent compiler error */
> >      }
> > -    g_free(cmd);
> >  }
> > 
> >  char *virtio_9p_test_path(const char *path)
> > @@ -209,8 +212,8 @@ static void *virtio_9p_pci_create(void *pci_bus,
> > QGuestAllocator *t_alloc, static void regex_replace(GString *haystack,
> > const char *pattern, const char *replace_fmt, ...)
> >  {
> > -    GRegex *regex;
> > -    char *replace, *s;
> > +    g_autoptr(GRegex) regex = NULL;
> > +    g_autofree char *replace = NULL, *s = NULL;
> >      va_list argp;
> > 
> >      va_start(argp, replace_fmt);
> > @@ -220,9 +223,6 @@ static void regex_replace(GString *haystack, const char
> > *pattern, regex = g_regex_new(pattern, 0, 0, NULL);
> >      s = g_regex_replace(regex, haystack->str, -1, 0, replace, 0, NULL);
> >      g_string_assign(haystack, s);
> > -    g_free(s);
> > -    g_regex_unref(regex);
> > -    g_free(replace);
> >  }
> > 
> >  void virtio_9p_assign_local_driver(GString *cmd_line, const char *args)
> 
> 

Re: [PATCH v2] tests/9pfs: Use g_autofree and g_autoptr where possible

[Christian Schoenebeck]

On Dienstag, 1. Februar 2022 11:11:37 CET Greg Kurz wrote:
> On Mon, 31 Jan 2022 18:43:22 +0100
> 
> Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> > On Montag, 31. Januar 2022 17:39:30 CET Greg Kurz wrote:
> > > It is recommended to use g_autofree or g_autoptr as it reduces
> > > the odds of introducing memory leaks in future changes. Let's do
> > > that everywhere a glib allocation is performed.
> > > 
> > > The virtio_9p_create_local_test_dir() function needs some extra
> > > care though : the template pointer is eventually cached into the
> > > local_test_path global variable for the duration of the tests and
> > > should not be freed. Add the g_autofree annotation but negate it
> > > with g_steal_pointer() to make it clear that the pointer ownership
> > > is dropped on purpose.
> > > 
> > > Based-on:
> > > <f6602123c6f7d0d593466231b04fba087817abbd.1642879848.git.qemu_oss@crudeb
> > > yte
> > > .com> Signed-off-by: Greg Kurz <groug@kaod.org>
> > > ---
> > > v2: - fix crash with local_test_path
> > > ---
> > > 
> > >  tests/qtest/libqos/virtio-9p.c | 30 +++++++++++++++---------------
> > >  1 file changed, 15 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/tests/qtest/libqos/virtio-9p.c
> > > b/tests/qtest/libqos/virtio-9p.c index ef96ef006adc..f0ffbc583492
> > > 100644
> > > --- a/tests/qtest/libqos/virtio-9p.c
> > > +++ b/tests/qtest/libqos/virtio-9p.c
> > > @@ -37,18 +37,22 @@ static char *concat_path(const char* a, const char*
> > > b)
> > > 
> > >      return g_build_filename(a, b, NULL);
> > >  
> > >  }
> > > 
> > > -void virtio_9p_create_local_test_dir(void)
> > > +static char *make_temp_dir(char *template)
> > > 
> > >  {
> > > 
> > > -    struct stat st;
> > > -    char *pwd = g_get_current_dir();
> > > -    char *template = concat_path(pwd, "qtest-9p-local-XXXXXX");
> > > -
> > > -    local_test_path = mkdtemp(template);
> > > -    if (!local_test_path) {
> > > +    char *path = mkdtemp(template);
> > > +    if (!path) {
> > > 
> > >          g_test_message("mkdtemp('%s') failed: %s", template,
> > > 
> > > strerror(errno)); }
> > > -    g_free(pwd);
> > > +    return path;
> > > +}
> > > +
> > > +void virtio_9p_create_local_test_dir(void)
> > > +{
> > > +    g_autofree char *pwd = g_get_current_dir();
> > > +    g_autofree char *template = concat_path(pwd,
> > > "qtest-9p-local-XXXXXX");
> > > +    struct stat st;
> > > 
> > > +    local_test_path = make_temp_dir(g_steal_pointer(&template));
> > 
> > Quite noisy diff and under the bottom line, it does not fix what it
> > originally supposed to: addressing the leak of the global variable
> > 'local_test_path'. g_steal_pointer() simply makes the previous g_autofree
> > prefix pointless.
> The g_autofree and g_steal_pointer() dance is just an idiom that
> says "I'm not freeing this pointer on purpose, it will be handled
> somewhere else". No big deal. I'll split this in two patches : one
> for the leak of 'local_test_path' with a clear comment instead of
> g_autofree and one for the remaining g_auto* conversions.

Yeah, I got that, but it still adds redundant code, as if adding a constant
literal expression like "... * 1/2 * 2".

The other changes have an actual purpose: they reduce code. This one though
just adds noise without a real purpose, plus it reverts of what I just have
done with the previous patch: getting rid of the previously already existing
separate function init_local_test_path():

https://github.com/cschoenebeck/qemu/commit/072636e2a9f3a153078e6046e52ae5a330728b68

I don't care enough though to continue defending my position on this.

> > Why not just moving g_autofree from 'template' to the global variable
> > 'local_test_path' and avoid all that noise?
> 
> Because the 'cleanup' attribute cannot be set on a static variable as
> documented in GCC:
> 
> cleanup (cleanup_function)
> 
>     The cleanup attribute runs a function when the variable goes out of
>     scope. This attribute can only be applied to auto function scope
>     variables; it may not be applied to parameters or variables with
>     static storage duration. The function must take one parameter, a
>     pointer to a type compatible with the variable. The return value
>     of the function (if any) is ignored.
> 
> and trying to do so produces:
> 
> ../../tests/qtest/libqos/virtio-9p.c:32:1: error: ‘cleanup’ attribute
> ignored [-Werror=attributes] 32 | static g_autofree char *local_test_path;
> 
>       | ^~~~~~
> 
> cc1: all warnings being treated as errors
> 
> The leak of 'local_test_path' can only be addressed with a g_free()
> in its last user, i.e. virtio_9p_remove_local_test_dir().

Agreed, that would probably be the best solution for now.

Thanks!

Best regards,
Christian Schoenebeck