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

[Pino Toscano]

On Tuesday, 12 September 2017 15:08:28 CEST Richard W.M. Jones wrote:
> 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)
>   ...
> 
> ?

It will, although it feels a bit awkward for the function to progress
if it is in an error situation already.

> > > +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).

D'oh, missed it, thanks for spotting it (and for writing it).

-- 
Pino Toscano
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: This is a digitally signed message part.
URL: <http://listman.redhat.com/archives/libguestfs/attachments/20170912/bbc2e2cd/attachment.sig>