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Re: [PATCH v20210601 04/38] tools: add readv_exact to libxenctrl

  • To: Juergen Gross <jgross@xxxxxxxx>
  • From: Olaf Hering <olaf@xxxxxxxxx>
  • Date: Mon, 7 Jun 2021 13:31:33 +0200
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
  • Delivery-date: Mon, 07 Jun 2021 11:32:00 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

Am Wed, 2 Jun 2021 13:41:02 +0200
schrieb Juergen Gross <jgross@xxxxxxxx>:

> Shouldn't you check for zero length iovec elements as in the
> writev_exact() case then?

It is not clear to me what the purpose of skipping zero-length iov's at the 
beginning of the iov array in writev_exact is.

I assume the syscall (or libc) will just skip them anyway. The code would not 
handle empty iov's in the middle of the array. Perhaps writev_exact should be 
done in the same way as my readv_exact, that would also remove the need for 
malloc. I think in the past I had a patch to do just that. Maybe just locally, 
maybe I sent it to this list.

In case of readv_exact, only the trailing incomplete iov will be filled with 
read_exact. I think the length parameter for read_exact can not become zero, 
"len" would already be zero. Zero-length iov's will be skipped by the loop 


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