[libvirt] [PATCH] avoid a probable EINVAL from lseek

[Daniel P. Berrange]

On Mon, Feb 01, 2010 at 10:18:27PM +0100, Jim Meyering wrote:
> 
> In src/qemu/qemu_driver.c, coverity reports this:
> 
>   Event negative_return_fn: Called negative-returning function "lseek(logfile, 0L, 2)"
>   Event var_assign: NEGATIVE return value of "lseek" assigned to signed variable "pos"
>   At conditional (1): "(pos = lseek(logfile, 0L, 2)) < 0" taking true path
>   2877 	    if ((pos = lseek(logfile, 0, SEEK_END)) < 0)
>   2878 	        VIR_WARN(_("Unable to seek to end of logfile: %s"),
>   2879 	                 virStrerror(errno, ebuf, sizeof ebuf));

I think it'd be less surprising to just set 'pos = 0' inside the if
branch here, so later code doesn't have to worry about unexpected
negative values.

> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 22593bf..676a27b 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -558,8 +558,8 @@ qemudLogReadFD(virConnectPtr conn, const char* logDir, const char* name, off_t p
>          close(fd);
>          return -1;
>      }
> -    if (lseek(fd, pos, SEEK_SET) < 0) {
> -        virReportSystemError(conn, errno,
> +    if (pos < 0 || lseek(fd, pos, SEEK_SET) < 0) {
> +      virReportSystemError(conn, pos < 0 ? 0 : errno,
>                               _("Unable to seek to %lld in %s"),
>                               (long long) pos, logfile);
>          close(fd);
> --

Daniel
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