Re: [Qemu-devel] [PATCH v2] linux-user: Use *at functions instead of caching interp_prefix contents

[Peter Maydell]

On 5 December 2017 at 04:48, Richard Henderson
<address@hidden> wrote:
> From: Richard Henderson <address@hidden>
>
> If the interp_prefix is a complete chroot, it may have a *lot* of files.
> Setting up the cache for this is quite expensive.  Instead, use the *at
> versions of various syscalls to attempt the operation in the prefix.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>
> Changes since v1 (Nov 2016):
>   * Require interp_dirfd set before trying the *at path.
>
>
> r~
> ---
>  linux-user/qemu.h    |   1 +
>  linux-user/elfload.c |  12 ++-
>  linux-user/main.c    |   3 +-
>  linux-user/syscall.c | 236 
> ++++++++++++++++++++++++++++++++++++++++++---------
>  4 files changed, 208 insertions(+), 44 deletions(-)
>
> diff --git a/linux-user/qemu.h b/linux-user/qemu.h
> index 4edd7d0c08..d04924fd2e 100644
> --- a/linux-user/qemu.h
> +++ b/linux-user/qemu.h
> @@ -437,6 +437,7 @@ void mmap_fork_start(void);
>  void mmap_fork_end(int child);
>
>  /* main.c */
> +extern int interp_dirfd;
>  extern unsigned long guest_stack_size;
>
>  /* user access */
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 20f3d8c2c3..5d3f7aa11d 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2203,7 +2203,17 @@ static void load_elf_interp(const char *filename, 
> struct image_info *info,
>  {
>      int fd, retval;
>
> -    fd = open(path(filename), O_RDONLY);
> +    switch (interp_dirfd > 0 && filename[0] == '/') {
> +    case true:

gcc doesn't like this pattern:

/home/petmay01/linaro/qemu-from-laptop/qemu/linux-user/syscall.c: In
function ‘do_name_to_handle_at’:
/home/petmay01/linaro/qemu-from-laptop/qemu/linux-user/syscall.c:7231:13:
error: switch condition has boolean value [-Werror=switch-bool]
     switch (interp_dirfd > 0 && name[0] == '/') {
             ^

It seems like an odd way to write an if().

thanks
-- PMM