[PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Andrew Cooper]

Otherwise, if it is not used, libxl_ctx_free() will close fd 0.

Reported-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
---
 tools/libxl/libxl.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 3526539..a1e0b5e 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -71,6 +71,7 @@ int libxl_ctx_alloc(libxl_ctx **pctx, int version,
     ctx->childproc_user = 0;
         
     ctx->sigchld_selfpipe[0] = -1;
+    ctx->sigchld_selfpipe[1] = -1;
     libxl__ev_fd_init(&ctx->sigchld_selfpipe_efd);
 
     /* The mutex is special because we can't idempotently destroy it */
-- 
1.7.10.4

Re: [PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Alex Bligh]

On 18/08/2014 14:02, Andrew Cooper wrote:
> Otherwise, if it is not used, libxl_ctx_free() will close fd 0.

Is there some way to work around this on the caller side
without a library change? Perhaps something that forces
sigchld_selfpipe to be opened?

Alex


> Reported-by: Alex Bligh <alex@alex.org.uk>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Ian Campbell <Ian.Campbell@citrix.com>
> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
> ---
>  tools/libxl/libxl.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 3526539..a1e0b5e 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -71,6 +71,7 @@ int libxl_ctx_alloc(libxl_ctx **pctx, int version,
>      ctx->childproc_user = 0;
>          
>      ctx->sigchld_selfpipe[0] = -1;
> +    ctx->sigchld_selfpipe[1] = -1;
>      libxl__ev_fd_init(&ctx->sigchld_selfpipe_efd);
>  
>      /* The mutex is special because we can't idempotently destroy it */
> 


-- 
Alex Bligh

Re: [PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Andrew Cooper]

On 18/08/14 14:10, Alex Bligh wrote:
> On 18/08/2014 14:02, Andrew Cooper wrote:
>> Otherwise, if it is not used, libxl_ctx_free() will close fd 0.
> Is there some way to work around this on the caller side
> without a library change? Perhaps something that forces
> sigchld_selfpipe to be opened?
>
> Alex

It looks like a call to libxl_childproc_setmode() will properly set up
both halves of ctx->sigchld_selfpipe[]

The call is to do with setting up the ownership of SIGCHILD in the
process, and a call to libxl_childproc_setmode(ctx, NULL, 0) should be
fine if you dont plan to fork in your own code.

~Andrew

>
>
>> Reported-by: Alex Bligh <alex@alex.org.uk>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> CC: Ian Campbell <Ian.Campbell@citrix.com>
>> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
>> ---
>>  tools/libxl/libxl.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
>> index 3526539..a1e0b5e 100644
>> --- a/tools/libxl/libxl.c
>> +++ b/tools/libxl/libxl.c
>> @@ -71,6 +71,7 @@ int libxl_ctx_alloc(libxl_ctx **pctx, int version,
>>      ctx->childproc_user = 0;
>>          
>>      ctx->sigchld_selfpipe[0] = -1;
>> +    ctx->sigchld_selfpipe[1] = -1;
>>      libxl__ev_fd_init(&ctx->sigchld_selfpipe_efd);
>>  
>>      /* The mutex is special because we can't idempotently destroy it */
>>
>

Re: [PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Alex Bligh]

On 18/08/2014 14:19, Andrew Cooper wrote:
> It looks like a call to libxl_childproc_setmode() will properly set up
> both halves of ctx->sigchld_selfpipe[]
> 
> The call is to do with setting up the ownership of SIGCHILD in the
> process, and a call to libxl_childproc_setmode(ctx, NULL, 0) should be
> fine if you dont plan to fork in your own code.

That does not appear to make any difference.

As far as I can see I need to ensure libxl__sigchld_needed gets called,
which means I need to ensure perhaps_sigchld_needed gets called
and chldmode_ours returns true. As 'creating' is false, in
libxl_sigchld_owner_libxl mode, I appear to need a child for
this to work. I can set it to libxl_sigchld_owner_libxl_always
or libxl_sigchld_owner_libxl_always_selective_reap and then
set it back. The code below is the minimum I can find that gets it
to work:

#include <stdio.h>
#include <stdlib.h>
#include <libxl.h>

#define LIBXL_API_VERSION 0x040200

/* compile with:
 * gcc -g -O0 xentest.c -o xentest -lxenlight
 */

void
fixctx (libxl_ctx *ctx)
{
  const libxl_childproc_hooks libxl_child_hooks = {
    .chldowner = libxl_sigchld_owner_libxl_always
  };
  libxl_childproc_setmode (ctx, &libxl_child_hooks, 0);
  libxl_childproc_setmode (ctx, NULL, 0);
}

void
test ()
{
  libxl_ctx *ctx = NULL;
  if (libxl_ctx_alloc (&ctx, LIBXL_VERSION, XTL_NONE, NULL))
    {
      fprintf (stderr, "libxl_ctx_alloc failed");
      exit (1);
    }
  fixctx (ctx);
  libxl_ctx_free (ctx);
}

int
main (int argc, char **argv)
{
  printf ("Before:\n");
  system ("ls -la /proc/self/fd");
  test ();
  printf ("\nAfter:\n");
  system ("ls -la /proc/self/fd");
  exit (0);
}

-- 
Alex Bligh

Re: [PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Andrew Cooper]

On 18/08/2014 14:02, Andrew Cooper wrote:
> Otherwise, if it is not used, libxl_ctx_free() will close fd 0.
>
> Reported-by: Alex Bligh <alex@alex.org.uk>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Ian Campbell <Ian.Campbell@citrix.com>
> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
> ---

Ping?  This is a rather nasty bug which needs fixing in 4.4 as well.

>  tools/libxl/libxl.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 3526539..a1e0b5e 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -71,6 +71,7 @@ int libxl_ctx_alloc(libxl_ctx **pctx, int version,
>      ctx->childproc_user = 0;
>          
>      ctx->sigchld_selfpipe[0] = -1;
> +    ctx->sigchld_selfpipe[1] = -1;
>      libxl__ev_fd_init(&ctx->sigchld_selfpipe_efd);
>  
>      /* The mutex is special because we can't idempotently destroy it */

Re: [PATCH] tools/libxl: Initialise both parts of ctx->sigchld_selfpipe[] to -1

[Ian Campbell]

On Mon, 2014-08-18 at 14:02 +0100, Andrew Cooper wrote:
> Otherwise, if it is not used, libxl_ctx_free() will close fd 0.
> 
> Reported-by: Alex Bligh <alex@alex.org.uk>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Ian Campbell <Ian.Campbell@citrix.com>
> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>

Acked + applied, thanks.

Ian.