Re: [Qemu-devel] [RFC PATCH 05/11] qemu_fclose: return last_error if set

[Eduardo Habkost]

On Wed, Nov 02, 2011 at 08:33:05AM +0100, Paolo Bonzini wrote:
> On 11/01/2011 08:20 PM, Eduardo Habkost wrote:
> >+/** Calls close function and set last_error if needed
> >+ *
> >+ * Internal function. qemu_fflush() must be called before this.
> >+ *
> >+ * Returns f->close() return value, or 0 if close function is not set.
> >+ */
> >+static int qemu_close(QEMUFile *f)
> >  {
> >      int ret = 0;
> >-    qemu_fflush(f);
> >-    if (f->close)
> >+    if (f->close) {
> >          ret = f->close(f->opaque);
> >+        qemu_file_set_if_error(f, ret);
> >+    }
> >+    return ret;
> >+}
> >+
> >+/** Closes the file
> >+ *
> >+ * Returns negative error value if any error happened on previous 
> >operations or
> >+ * while closing the file. Returns 0 or positive number on success.
> >+ *
> >+ * The meaning of return value on success depends on the specific backend
> >+ * being used.
> >+ */
> >+int qemu_fclose(QEMUFile *f)
> >+{
> >+    int ret;
> >+    qemu_fflush(f);
> >+    ret = qemu_close(f);
> 
> Isn't the return value of qemu_close useless, because if nonzero it
> will always be present in last_error too?  With this change, I'd
> leave it inline.

No, if it's positive it won't be set on last_error, so we have to save
it somewhere other than last_error (that's what the qemu_close() return
value is used for).


It could be inlined, yes. I just wanted to isolate the "call f->close if
set, handling errors" part from the flush+close+g_free logic, to try to
make functions shorter and easier to read and analyze (please let me
know if I failed to do that :-).


Without a separate function and qemu_file_set_if_error(), the function
will look like:

int qemu_fclose(QEMUFile *f)
{
    int ret = 0;
    qemu_fflush();
    if (f->close) {
        ret = f->close(f->opaque);
    }
    if (f->last_error) {
        ret = f->last_error;
    }
    g_free(f);
    return ret;
}


Now that I am looking at the resulting code, it doesn't look too bad. I
guess I was simply too eager to encapsulate every bit of logic (in this
case the "if (f->close) ..." part) into separate functions. I find the
two-function version slightly easier to analyze, though.

I am happy with either version, so I am open to suggestions.


> 
> >+    if (f->last_error)
> >+        ret = f->last_error;

Oops, I have to fix coding style and add braces here.

> >      g_free(f);
> >      return ret;
> 
> Paolo
> 

-- 
Eduardo