On Mon, Nov 02, 2015 at 05:13:14PM +0800, Xiao Guangrong wrote:
> lseek can not work for all block devices as the man page says:
> | Some devices are incapable of seeking and POSIX does not specify
> | which devices must support lseek().
>
> This patch tries to add the support on Linux by using BLKGETSIZE64
> ioctl
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
On which cases is this patch necessary? Do you know any examples of
Linux block devices that won't work with lseek(SEEK_END)?
> ---
> util/osdep.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/util/osdep.c b/util/osdep.c
> index 5a61e19..b20c793 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -45,6 +45,11 @@
> extern int madvise(caddr_t, size_t, int);
> #endif
>
> +#ifdef CONFIG_LINUX
> +#include <sys/ioctl.h>
> +#include <linux/fs.h>
> +#endif
> +
> #include "qemu-common.h"
> #include "qemu/sockets.h"
> #include "qemu/error-report.h"
> @@ -433,6 +438,21 @@ int64_t qemu_fd_getlength(int fd)
> {
> int64_t size;
>
> +#ifdef CONFIG_LINUX
> + struct stat stat_buf;
> + if (fstat(fd, &stat_buf) < 0) {
> + return -errno;
> + }
> +
> + if ((S_ISBLK(stat_buf.st_mode)) && !ioctl(fd, BLKGETSIZE64, &size)) {
> + /* The size of block device is larger than max int64_t? */
> + if (size < 0) {
> + return -EOVERFLOW;
> + }
> + return size;
> + }
> +#endif
> +
> size = lseek(fd, 0, SEEK_END);
> if (size < 0) {
> return -errno;
> --
> 1.8.3.1
>
--
Eduardo
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