[Libguestfs] [PATCH v2 2/5] lib: qemu: Factor out common code for reading and writing cache files.

[Richard W.M. Jones]

On Tue, Sep 12, 2017 at 03:05:43PM +0200, Pino Toscano wrote:
> On Tuesday, 12 September 2017 14:29:13 CEST Richard W.M. Jones wrote:
> > +/**
> > + * Generic functions for reading and writing the cache files, used
> > + * where we are just reading and writing plain text strings.
> > + */
> > +static int
> > +generic_read_cache (guestfs_h *g, const char *filename, char **strp)
> > +{
> > +  if (access (filename, R_OK) == -1 && errno == ENOENT)
> > +    return 0;                   /* no cache, run the test instead */
> 
> This will go ahead if access() failed for any other error though;
> IMHO a better check could be:
> 
>   if (access (filename, R_OK) == -1) {
>     if (errno == ENOENT)
>       return 0;                   /* no cache, run the test instead */
>     perrorf (g, "access: %s", filename);
>     return -1;
>   }

But isn't it OK since the following line will return the true error:

  if (guestfs_int_read_whole_file (g, filename, strp, NULL) == -1)
  ...

?

> > +static int
> > +generic_write_cache (guestfs_h *g, const char *filename, const char *str)
> > +{
> > +  CLEANUP_FCLOSE FILE *fp = fopen (filename, "w");
> > +  if (fp == NULL) {
> > +    perrorf (g, "%s", filename);
> > +    return -1;
> > +  }
> > +
> > +  if (fprintf (fp, "%s", str) == -1) {
> > +    perrorf (g, "%s: write", filename);
> > +    return -1;
> > +  }
> > +
> > +  return 0;
> > +}
> 
> While this is the same code already used, IMHO it would make more sense
> to use open/write directly (since we have a buffer already, it will be
> faster than using sprintf); there are snippets that call write() in a
> loop until the whole buffer is written in different parts of the
> library, so factorizing them could help.

OK (using full_write).

Rich.

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