Libguestfs - Nov 2017 - [nbdkit PATCH] file: Diagnose a missing file earlier

If a user typos the filename for the file plugin, they do not
find out about it until later when the first client gets an
abrupt hangup, when file_open() fails to open things.  Better
is to avoid starting a server at all if the file doesn't exist
yet.

While at it, avoid a memory leak if the caller passes a fileargument more than
once.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 plugins/file/file.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/plugins/file/file.c b/plugins/file/file.c
index ef5da3d..4a91251 100644
--- a/plugins/file/file.c
+++ b/plugins/file/file.c
@@ -117,6 +117,7 @@ file_config (const char *key, const char *value)
 {
   if (strcmp (key, "file") == 0) {
     /* See FILENAMES AND PATHS in nbdkit-plugin(3). */
+    free (filename);
     filename = nbdkit_absolute_path (value);
     if (!filename)
       return -1;
@@ -147,6 +148,10 @@ file_config_complete (void)
     nbdkit_error ("you must supply the file=<FILENAME> parameter
after the plugin name on the command line");
     return -1;
   }
+  if (access (filename, F_OK) < 0) {
+    nbdkit_error ("access '%s': %m", filename);
+    return -1;
+  }

   return 0;
 }
-- 
2.13.6

On Tue, Nov 21, 2017 at 04:45:14PM -0600, Eric Blake
wrote:
> If a user typos the filename for the file plugin, they do not
> find out about it until later when the first client gets an
> abrupt hangup, when file_open() fails to open things.  Better
> is to avoid starting a server at all if the file doesn't exist
> yet.
> 
> While at it, avoid a memory leak if the caller passes a file> argument
more than once.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  plugins/file/file.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/plugins/file/file.c b/plugins/file/file.c
> index ef5da3d..4a91251 100644
> --- a/plugins/file/file.c
> +++ b/plugins/file/file.c
> @@ -117,6 +117,7 @@ file_config (const char *key, const char *value)
>  {
>    if (strcmp (key, "file") == 0) {
>      /* See FILENAMES AND PATHS in nbdkit-plugin(3). */
> +    free (filename);
>      filename = nbdkit_absolute_path (value);
>      if (!filename)
>        return -1;
> @@ -147,6 +148,10 @@ file_config_complete (void)
>      nbdkit_error ("you must supply the file=<FILENAME>
parameter after the plugin name on the command line");
>      return -1;
>    }
> +  if (access (filename, F_OK) < 0) {
> +    nbdkit_error ("access '%s': %m", filename);
> +    return -1;
> +  }
> 
ACK.

Rich.

-- 
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