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Re: [libvirt] [PATCH] introduce VIR_CLOSE to be used rather than close()



2010/10/15 Stefan Berger <stefanb linux vnet ibm com>:
>  Since bugs due to double-closed filedescriptors are difficult to track down
> in a multi-threaded system, I am introducing the VIR_CLOSE(fd) macro to help
> avoid mistakes here.
>
> There are lots of places where close() is being used. In this patch I am
> only cleaning up usage of close() in src/conf where the problems were.
>
> I also dare to declare close() as being deprecated in libvirt code base
> (HACKING). :-)
>
> Signed-off-by: Stefan Berger <stefanb us ibm com>
>
> ---
>  HACKING                            |   11 +++++++++++
>  src/Makefile.am                    |    3 ++-
>  src/conf/domain_conf.c             |   14 ++++++++------
>  src/conf/network_conf.c            |    9 +++++----
>  src/conf/nwfilter_conf.c           |   17 +++++++++--------
>  src/conf/storage_conf.c            |    9 +++++----
>  src/conf/storage_encryption_conf.c |    5 +++--
>  src/util/files.c                   |   37
> +++++++++++++++++++++++++++++++++++++
>  src/util/files.h                   |   37
> +++++++++++++++++++++++++++++++++++++
>  9 files changed, 117 insertions(+), 25 deletions(-)
>
> Index: libvirt-acl/src/util/files.c
> ===================================================================
> --- /dev/null
> +++ libvirt-acl/src/util/files.c
> @@ -0,0 +1,37 @@
> +/*
> + * memory.c: safer file handling
> + *
> + * Copyright (C) 2010 IBM Corporation
> + * Copyright (C) 2010 Stefan Berger
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
> + *
> + */
> +
> +#include <unistd.h>
> +
> +#include "files.h"
> +
> +int virClose(int *fdptr)
> +{
> +    int rc;
> +
> +    if (*fdptr >= 0) {
> +        rc = close(*fdptr);
> +        *fdptr = -1;
> +    } else
> +        rc = 0;
> +    return rc;
> +}
> Index: libvirt-acl/src/util/files.h
> ===================================================================
> --- /dev/null
> +++ libvirt-acl/src/util/files.h
> @@ -0,0 +1,37 @@
> +/*
> + * files.h: safer file handling
> + *
> + * Copyright (C) 2010 IBM Corporation
> + * Copyright (C) 2010 Stefan Berger
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
> + *
> + */
> +
> +
> +#ifndef __VIR_FILES_H_
> +# define __VIR_FILES_H_
> +
> +# include "internal.h"
> +
> +/* Don't call these directly - use the macros below */
> +int virClose(int *fdptr);
> +
> +# define VIR_CLOSE(FD)      \
> +    virClose(&(FD))
> +
> +
> +#endif /* __VIR_FILES_H */
> +


> Index: libvirt-acl/src/conf/domain_conf.c
> ===================================================================
> --- libvirt-acl.orig/src/conf/domain_conf.c
> +++ libvirt-acl/src/conf/domain_conf.c
> @@ -46,6 +46,7 @@
>  #include "nwfilter_conf.h"
>  #include "ignore-value.h"
>  #include "storage_file.h"
> +#include "files.h"
>
>  #define VIR_FROM_THIS VIR_FROM_DOMAIN
>
> @@ -6798,17 +6799,18 @@ int virDomainSaveXML(const char *configD
>         goto cleanup;
>     }
>
> -    if (close(fd) < 0) {
> +    if (VIR_CLOSE(fd) < 0) {
>         virReportSystemError(errno,
>                              _("cannot save config file '%s'"),
>                              configFile);
> -        goto cleanup;
> +        goto cleanup_free;
>     }
>
>     ret = 0;
>  cleanup:
> -    if (fd != -1)
> -        close(fd);
> +    VIR_CLOSE(fd);
> +
> + cleanup_free:
>     VIR_FREE(configFile);
>     return ret;
>  }

Why did you add a new label here? You build VIR_CLOSE in a way that
allows safe double invocation. Therefore, this is just fine, isn't it:

-    if (close(fd) < 0) {
+    if (VIR_CLOSE(fd) < 0) {
         virReportSystemError(errno,
                              _("cannot save config file '%s'"),
                              configFile);
         goto cleanup;
     }
     ret = 0;

 cleanup:
-    if (fd != -1)
-        close(fd);
+    VIR_CLOSE(fd);
     VIR_FREE(configFile);
     return ret;
 }

This pattern reoccurs several times.

Matthias


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