block/gluster: add support to choose libgfapi logfile

currently all the libgfapi logs defaults to '/dev/stderr' as it was hardcoded
in a call to glfs logging api, in case if debug level is chosen to DEBUG/TRACE
gfapi logs will be huge and fill/overflow the console view.

this patch provides a commandline option to mention log file path which helps
in logging to the specified file and also help in persisting the gfapi logs.

Usage: -drive file=gluster://hostname/volname/image.qcow2,file.debug=9,\
                 file.logfile=/var/log/qemu/qemu-gfapi.log

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
---
 block/gluster.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

On Tue, Jul 05, 2016 at 02:46:26PM +0530, Prasanna Kumar Kalever wrote:
> currently all the libgfapi logs defaults to '/dev/stderr' as it was hardcoded
> in a call to glfs logging api, in case if debug level is chosen to DEBUG/TRACE
> gfapi logs will be huge and fill/overflow the console view.
> 
> this patch provides a commandline option to mention log file path which helps
> in logging to the specified file and also help in persisting the gfapi logs.
> 
> Usage: -drive file=gluster://hostname/volname/image.qcow2,file.debug=9,\
>                  file.logfile=/var/log/qemu/qemu-gfapi.log
> 
> Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
> ---
>  block/gluster.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/block/gluster.c b/block/gluster.c
> index 16f7778..6875429 100644
> --- a/block/gluster.c
> +++ b/block/gluster.c
> @@ -24,6 +24,7 @@ typedef struct GlusterAIOCB {
>  typedef struct BDRVGlusterState {
>      struct glfs *glfs;
>      struct glfs_fd *fd;
> +    const char *logfile;

Having this const looks incorrect; we want a copy of the string.  After the
opts are deleted, the string this points to has been freed.

>      bool supports_seek_data;
>      int debug_level;
>  } BDRVGlusterState;
> @@ -34,6 +35,7 @@ typedef struct GlusterConf {
>      char *volname;
>      char *image;
>      char *transport;
> +    const char *logfile;

Here too, this is probably best not being const.

>      int debug_level;
>  } GlusterConf;
>  
> @@ -181,7 +183,8 @@ static struct glfs *qemu_gluster_init(GlusterConf *gconf, const char *filename,
>      ret = qemu_gluster_parseuri(gconf, filename);
>      if (ret < 0) {
>          error_setg(errp, "Usage: file=gluster[+transport]://[server[:port]]/"
> -                   "volname/image[?socket=...]");
> +                   "volname/image[?socket=...][,file.debug=N]"
> +                   "[,file.logfile=/path/filename.log]");
>          errno = -ret;
>          goto out;
>      }
> @@ -197,7 +200,7 @@ static struct glfs *qemu_gluster_init(GlusterConf *gconf, const char *filename,
>          goto out;
>      }
>  
> -    ret = glfs_set_logging(glfs, "-", gconf->debug_level);
> +    ret = glfs_set_logging(glfs, gconf->logfile, gconf->debug_level);
>      if (ret < 0) {
>          goto out;
>      }
> @@ -256,6 +259,8 @@ static void gluster_finish_aiocb(struct glfs_fd *fd, ssize_t ret, void *arg)
>  }
>  
>  #define GLUSTER_OPT_FILENAME "filename"
> +#define GLUSTER_OPT_LOGFILE "logfile"
> +#define GLUSTER_LOGFILE_DEFAULT "-" /* '-' handled in libgfapi as /dev/stderr */
>  #define GLUSTER_OPT_DEBUG "debug"
>  #define GLUSTER_DEBUG_DEFAULT 4
>  #define GLUSTER_DEBUG_MAX 9
> @@ -271,6 +276,11 @@ static QemuOptsList runtime_opts = {
>              .help = "URL to the gluster image",
>          },
>          {
> +            .name = GLUSTER_OPT_LOGFILE,
> +            .type = QEMU_OPT_STRING,
> +            .help = "Logfile path of libgfapi",
> +        },
> +        {
>              .name = GLUSTER_OPT_DEBUG,
>              .type = QEMU_OPT_NUMBER,
>              .help = "Gluster log level, valid range is 0-9",
> @@ -339,6 +349,12 @@ static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
>  
>      filename = qemu_opt_get(opts, GLUSTER_OPT_FILENAME);
>  
> +    s->logfile = qemu_opt_get(opts, GLUSTER_OPT_LOGFILE);
> +    if (!s->logfile) {
> +            s->logfile = GLUSTER_LOGFILE_DEFAULT;
> +    }
> +    gconf->logfile = s->logfile;
> +

At the end of qemu_gluster_open(),  qemu_opts_del() is called, which means
the const char * s->logfile will end up pointing at freed memory.

>      s->debug_level = qemu_opt_get_number(opts, GLUSTER_OPT_DEBUG,
>                                           GLUSTER_DEBUG_DEFAULT);
>      if (s->debug_level < 0) {
> @@ -422,6 +438,7 @@ static int qemu_gluster_reopen_prepare(BDRVReopenState *state,
>  
>      gconf = g_new0(GlusterConf, 1);
>  
> +    gconf->logfile = s->logfile;
>      gconf->debug_level = s->debug_level;
>      reop_s->glfs = qemu_gluster_init(gconf, state->bs->filename, errp);
>      if (reop_s->glfs == NULL) {
> @@ -556,6 +573,11 @@ static int qemu_gluster_create(const char *filename,
>      char *tmp = NULL;
>      GlusterConf *gconf = g_new0(GlusterConf, 1);
>  
> +    gconf->logfile = qemu_opt_get_del(opts, GLUSTER_OPT_LOGFILE);

In this case, qemu_opt_get_del() returns a malloc'ed string, so we must make
sure to free it after usage.

> +    if (!gconf->logfile) {
> +            gconf->logfile = GLUSTER_LOGFILE_DEFAULT;
> +    }
> +
>      gconf->debug_level = qemu_opt_get_number_del(opts, GLUSTER_OPT_DEBUG,
>                                                   GLUSTER_DEBUG_DEFAULT);
>      if (gconf->debug_level < 0) {
> @@ -949,6 +971,11 @@ static QemuOptsList qemu_gluster_create_opts = {
>              .help = "Preallocation mode (allowed values: off, full)"
>          },
>          {
> +            .name = GLUSTER_OPT_LOGFILE,
> +            .type = QEMU_OPT_STRING,
> +            .help = "Logfile path of libgfapi",
> +        },
> +        {
>              .name = GLUSTER_OPT_DEBUG,
>              .type = QEMU_OPT_NUMBER,
>              .help = "Gluster log level, valid range is 0-9",
> -- 
> 2.7.4
>