Re: [Xen-devel] [PATCH v2] tools/xenstore: try to get minimum thread stack size for watch thread

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 26, 2018 at 09:46:12AM +0100, Juergen Gross wrote:
> When creating a pthread in xs_watch() try to get the minimal needed
> size of the thread from glibc instead of using a constant. This avoids
> problems when the library is used in programs with large per-thread
> memory.
> 
> Use dlsym() to get the pointer to __pthread_get_minstack() in order to
> avoid linkage problems and fall back to the current constant size if
> not found.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V2:
> - use _GNU_SOURCE (Wei Liu)
> - call __pthread_get_minstack() with parameter
> - add -ldl to correct make flags
> - ensure to not using smaller stack size than today
> ---
>  tools/xenstore/Makefile |  4 ++++
>  tools/xenstore/xs.c     | 21 ++++++++++++++++++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
> index 2b99d2bc1b..0831be0b6f 100644
> --- a/tools/xenstore/Makefile
> +++ b/tools/xenstore/Makefile
> @@ -100,6 +100,10 @@ libxenstore.so.$(MAJOR): libxenstore.so.$(MAJOR).$(MINOR)
>       ln -sf $< $@
>  
>  xs.opic: CFLAGS += -DUSE_PTHREAD
> +ifeq ($(CONFIG_Linux),y)
> +xs.opic: CFLAGS += -DUSE_DLSYM
> +libxenstore.so.$(MAJOR).$(MINOR): LDFLAGS += -ldl
> +endif
>  
>  libxenstore.so.$(MAJOR).$(MINOR): xs.opic xs_lib.opic
>       $(CC) $(LDFLAGS) $(PTHREAD_LDFLAGS) -Wl,$(SONAME_LDFLAG) 
> -Wl,libxenstore.so.$(MAJOR) $(SHLIB_LDFLAGS) -o $@ $^ 
> $(LDLIBS_libxentoolcore) $(SOCKET_LIBS) $(PTHREAD_LIBS) $(APPEND_LDFLAGS)
> diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
> index abffd9cd80..77700bff2b 100644
> --- a/tools/xenstore/xs.c
> +++ b/tools/xenstore/xs.c
> @@ -16,6 +16,8 @@
>      License along with this library; If not, see 
> <http://www.gnu.org/licenses/>.
>  */
>  
> +#define _GNU_SOURCE
> +
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <fcntl.h>
> @@ -47,6 +49,10 @@ struct xs_stored_msg {
>  
>  #include <pthread.h>
>  
> +#ifdef USE_DLSYM
> +#include <dlfcn.h>
> +#endif
> +
>  struct xs_handle {
>       /* Communications channel to xenstore daemon. */
>       int fd;
> @@ -810,12 +816,25 @@ bool xs_watch(struct xs_handle *h, const char *path, 
> const char *token)
>       if (!h->read_thr_exists) {
>               sigset_t set, old_set;
>               pthread_attr_t attr;
> +             static size_t stack_size;
> +#ifdef USE_DLSYM
> +             size_t (*getsz)(pthread_attr_t *attr);
> +#endif
>  
>               if (pthread_attr_init(&attr) != 0) {
>                       mutex_unlock(&h->request_mutex);
>                       return false;
>               }
> -             if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 
> 0) {
> +             if (!stack_size) {
> +#ifdef USE_DLSYM
> +                     getsz = dlsym(RTLD_DEFAULT, "__pthread_get_minstack");

dlsym is part of libc in FreeBSD, so it can be used but there's no ldl
library (so passing -ldl to the linker is going to throw an error).

I guess it would be nice to have a configure test for this, but I'm
not going to argue over it.

Roger.

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