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Date: Thu, 8 Jun 2017 09:07:48 +0800
From: Haozhong Zhang <haozhong.zhang@intel.com>
Message-ID: <20170608010748.jqcdbcnt44pvqjsr@hz-desktop>
References: <20170606072229.9302-1-haozhong.zhang@intel.com>
	<20170606072229.9302-3-haozhong.zhang@intel.com>
	<20170607151445.GE21990@stefanha-x1.localdomain>
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Subject: Re: [Qemu-devel] [PATCH v2 2/4] nvdimm: warn if the backend is not
 a DAX device
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Xiao Guangrong <guangrong.xiao@gmail.com>, Dan Williams <dan.j.williams@intel.com>

On 06/07/17 16:14 +0100, Stefan Hajnoczi wrote:
> On Tue, Jun 06, 2017 at 03:22:27PM +0800, Haozhong Zhang wrote:
> > diff --git a/util/osdep.c b/util/osdep.c
> > index a2863c8e53..02881f96bc 100644
> > --- a/util/osdep.c
> > +++ b/util/osdep.c
> > @@ -471,3 +471,64 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
> >      return readv_writev(fd, iov, iov_cnt, true);
> >  }
> >  #endif
> > +
> > +#ifdef __linux__
> > +static ssize_t qemu_dev_dax_sysfs_read(int fd, const char *entry,
> > +                                       char *buf, size_t len)
> > +{
> > +    ssize_t read_bytes;
> > +    struct stat st;
> > +    unsigned int major, minor;
> > +    char *path, *pos;
> > +    int sysfs_fd;
> > +
> > +    if (fstat(fd, &st)) {
> > +        return 0;
> > +    }
> > +
> > +    major = major(st.st_rdev);
> > +    minor = minor(st.st_rdev);
> > +    path = g_strdup_printf("/sys/dev/char/%u:%u/%s", major, minor, entry);
> > +
> > +    sysfs_fd = open(path, O_RDONLY);
> > +    g_free(path);
> > +    if (sysfs_fd == -1) {
> > +        return 0;
> > +    }
> > +
> > +    read_bytes = read(sysfs_fd, buf, len - 1);
> > +    close(sysfs_fd);
> > +    if (read_bytes > 0) {
> > +        buf[read_bytes] = '\0';
> > +        pos = g_strstr_len(buf, read_bytes, "\n");
> > +        if (pos) {
> > +            *pos = '\0';
> > +        }
> 
> Should read_bytes be adjusted since we made the string shorter?

Yes, I'll change in the next version.

Thanks,
Haozhong