Re: [Qemu-devel] [PATCH] use g_path_get_basename instead of basename

[Alex Williamson]

On Thu,  1 Mar 2018 10:08:06 +0300
Julia Suvorova via Qemu-devel <address@hidden> wrote:

> basename(3) and dirname(3) modify their argument and may return
> pointers to statically allocated memory which may be overwritten by
> subsequent calls.
> g_path_get_basename and g_path_get_dirname have no such issues, and
> therefore more preferable.

I think it's quite a bit arguable whether it's preferable, afaict there
are no bugs fixed here.  The basic functions are being used correctly
and are more conservative of memory usage than the glib variants.  In
several cases below the basic functions seem far more efficient and we
don't need to worry about freeing unnecessarily allocated memory, the
diffstat seems to attest to this.  Is the inefficiency and possibility
of leaking unintentionally allocated memory a statistical improvement
over the claimed perils of these absolutely standard and well known
functions?

I know mine is a losing battle against glib, but the changelog might as
well just say "Succumb to glib" because I fail to see that there's
actually an improvement here.  If Paolo wants to take this,

Acked-by: Alex Williamson <address@hidden>

Thanks,
Alex
 
> Signed-off-by: Julia Suvorova <address@hidden>
> ---
>  fsdev/virtfs-proxy-helper.c |  6 +++++-
>  hw/s390x/s390-ccw.c         | 17 +++++++++++------
>  hw/vfio/ccw.c               |  7 +++++--
>  hw/vfio/pci.c               |  6 ++++--
>  hw/vfio/platform.c          |  6 ++++--
>  qemu-io.c                   |  8 +++++++-
>  qemu-nbd.c                  |  5 ++++-
>  qga/commands-posix.c        |  4 ++--
>  8 files changed, 42 insertions(+), 17 deletions(-)
> 
> diff --git a/fsdev/virtfs-proxy-helper.c b/fsdev/virtfs-proxy-helper.c
> index 8e48500..da3452f 100644
> --- a/fsdev/virtfs-proxy-helper.c
> +++ b/fsdev/virtfs-proxy-helper.c
> @@ -787,6 +787,8 @@ error:
>  
>  static void usage(char *prog)
>  {
> +    char *base_filename = g_path_get_basename(prog);
> +
>      fprintf(stderr, "usage: %s\n"
>              " -p|--path <path> 9p path to export\n"
>              " {-f|--fd <socket-descriptor>} socket file descriptor to be 
> used\n"
> @@ -795,7 +797,9 @@ static void usage(char *prog)
>              " access to this socket\n"
>              " \tNote: -s & -f can not be used together\n"
>              " [-n|--nodaemon] Run as a normal program\n",
> -            basename(prog));
> +            base_filename);
> +
> +    g_free(base_filename);
>  }
>  
>  static int process_reply(int sock, int type,
> diff --git a/hw/s390x/s390-ccw.c b/hw/s390x/s390-ccw.c
> index 7fc1c60..460dbab 100644
> --- a/hw/s390x/s390-ccw.c
> +++ b/hw/s390x/s390-ccw.c
> @@ -34,7 +34,7 @@ static void s390_ccw_get_dev_info(S390CCWDevice *cdev,
>                                    Error **errp)
>  {
>      unsigned int cssid, ssid, devid;
> -    char dev_path[PATH_MAX] = {0}, *tmp;
> +    char dev_path[PATH_MAX] = {0}, *dir_name, *dir_path;
>  
>      if (!sysfsdev) {
>          error_setg(errp, "No host device provided");
> @@ -48,18 +48,23 @@ static void s390_ccw_get_dev_info(S390CCWDevice *cdev,
>          return;
>      }
>  
> -    cdev->mdevid = g_strdup(basename(dev_path));
> +    cdev->mdevid = g_path_get_basename(dev_path);
>  
> -    tmp = basename(dirname(dev_path));
> -    if (sscanf(tmp, "%2x.%1x.%4x", &cssid, &ssid, &devid) != 3) {
> -        error_setg_errno(errp, errno, "Failed to read %s", tmp);
> -        return;
> +    dir_path = g_path_get_dirname(dev_path);
> +    dir_name = g_path_get_basename(dir_path);
> +    if (sscanf(dir_name, "%2x.%1x.%4x", &cssid, &ssid, &devid) != 3) {
> +        error_setg_errno(errp, errno, "Failed to read %s", dir_name);
> +        goto out;
>      }
>  
>      cdev->hostid.cssid = cssid;
>      cdev->hostid.ssid = ssid;
>      cdev->hostid.devid = devid;
>      cdev->hostid.valid = true;
> +
> +out:
> +    g_free(dir_path);
> +    g_free(dir_name);
>  }
>  
>  static void s390_ccw_realize(S390CCWDevice *cdev, char *sysfsdev, Error 
> **errp)
> diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> index 16713f2..c0566a9 100644
> --- a/hw/vfio/ccw.c
> +++ b/hw/vfio/ccw.c
> @@ -300,7 +300,7 @@ static void vfio_put_device(VFIOCCWDevice *vcdev)
>  
>  static VFIOGroup *vfio_ccw_get_group(S390CCWDevice *cdev, Error **errp)
>  {
> -    char *tmp, group_path[PATH_MAX];
> +    char *tmp, *group_name, group_path[PATH_MAX];
>      ssize_t len;
>      int groupid;
>  
> @@ -317,10 +317,13 @@ static VFIOGroup *vfio_ccw_get_group(S390CCWDevice 
> *cdev, Error **errp)
>  
>      group_path[len] = 0;
>  
> -    if (sscanf(basename(group_path), "%d", &groupid) != 1) {
> +    group_name = g_path_get_basename(group_path);
> +    if (sscanf(group_name, "%d", &groupid) != 1) {
>          error_setg(errp, "vfio: failed to read %s", group_path);
> +        g_free(group_name);
>          return NULL;
>      }
> +    g_free(group_name);
>  
>      return vfio_get_group(groupid, &address_space_memory, errp);
>  }
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 033cc8d..ba03136 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -2807,7 +2807,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>          return;
>      }
>  
> -    vdev->vbasedev.name = g_strdup(basename(vdev->vbasedev.sysfsdev));
> +    vdev->vbasedev.name = g_path_get_basename(vdev->vbasedev.sysfsdev);
>      vdev->vbasedev.ops = &vfio_pci_ops;
>      vdev->vbasedev.type = VFIO_DEVICE_TYPE_PCI;
>      vdev->vbasedev.dev = &vdev->pdev.qdev;
> @@ -2824,11 +2824,13 @@ static void vfio_realize(PCIDevice *pdev, Error 
> **errp)
>  
>      group_path[len] = 0;
>  
> -    group_name = basename(group_path);
> +    group_name = g_path_get_basename(group_path);
>      if (sscanf(group_name, "%d", &groupid) != 1) {
>          error_setg_errno(errp, errno, "failed to read %s", group_path);
> +        g_free(group_name);
>          goto error;
>      }
> +    g_free(group_name);
>  
>      trace_vfio_realize(vdev->vbasedev.name, groupid);
>  
> diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
> index 0d4bc0a..15dbae8 100644
> --- a/hw/vfio/platform.c
> +++ b/hw/vfio/platform.c
> @@ -561,7 +561,7 @@ static int vfio_base_device_init(VFIODevice *vbasedev, 
> Error **errp)
>      /* @sysfsdev takes precedence over @host */
>      if (vbasedev->sysfsdev) {
>          g_free(vbasedev->name);
> -        vbasedev->name = g_strdup(basename(vbasedev->sysfsdev));
> +        vbasedev->name = g_path_get_basename(vbasedev->sysfsdev);
>      } else {
>          if (!vbasedev->name || strchr(vbasedev->name, '/')) {
>              error_setg(errp, "wrong host device name");
> @@ -590,11 +590,13 @@ static int vfio_base_device_init(VFIODevice *vbasedev, 
> Error **errp)
>  
>      group_path[len] = 0;
>  
> -    group_name = basename(group_path);
> +    group_name = g_path_get_basename(group_path);
>      if (sscanf(group_name, "%d", &groupid) != 1) {
>          error_setg_errno(errp, errno, "failed to read %s", group_path);
> +        g_free(group_name);
>          return -errno;
>      }
> +    g_free(group_name);
>  
>      trace_vfio_platform_base_device_init(vbasedev->name, groupid);
>  
> diff --git a/qemu-io.c b/qemu-io.c
> index 2c00ea0..1de5fc7 100644
> --- a/qemu-io.c
> +++ b/qemu-io.c
> @@ -308,6 +308,11 @@ static char *get_prompt(void)
>      return prompt;
>  }
>  
> +static void free_progname(void)
> +{
> +    g_free(progname);
> +}
> +
>  static void GCC_FMT_ATTR(2, 3) readline_printf_func(void *opaque,
>                                                      const char *fmt, ...)
>  {
> @@ -504,7 +509,8 @@ int main(int argc, char **argv)
>  #endif
>  
>      module_call_init(MODULE_INIT_TRACE);
> -    progname = basename(argv[0]);
> +    progname = g_path_get_basename(argv[0]);
> +    atexit(free_progname);
>      qemu_init_exec_dir(argv[0]);
>  
>      qcrypto_init(&error_fatal);
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index ed5d9b5..36bafe7 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -893,8 +893,11 @@ int main(int argc, char **argv)
>      }
>  
>      if (device != NULL && sockpath == NULL) {
> +        char *base_filename = g_path_get_basename(device);
> +
>          sockpath = g_malloc(128);
> -        snprintf(sockpath, 128, SOCKET_PATH, basename(device));
> +        snprintf(sockpath, 128, SOCKET_PATH, base_filename);
> +        g_free(base_filename);
>      }
>  
>      server = qio_net_listener_new();
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 9670614..53a29e3 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -808,7 +808,7 @@ static char *get_pci_driver(char const *syspath, int 
> pathlen, Error **errp)
>      len = readlink(dpath, buf, sizeof(buf) - 1);
>      if (len != -1) {
>          buf[len] = 0;
> -        driver = g_strdup(basename(buf));
> +        driver = g_path_get_basename(buf);
>      }
>      g_free(dpath);
>      g_free(path);
> @@ -1053,7 +1053,7 @@ static void build_guest_fsinfo_for_device(char const 
> *devpath,
>      }
>  
>      if (!fs->name) {
> -        fs->name = g_strdup(basename(syspath));
> +        fs->name = g_path_get_basename(syspath);
>      }
>  
>      g_debug("  parse sysfs path '%s'", syspath);