Re: [PATCH v4 3/6] linux-user: Add strace support for printing argument of syscalls used for extended attributes

[Laurent Vivier]

Le 16/06/2020 à 12:39, Filip Bozuta a écrit :
> From: Filip Bozuta <Filip.Bozuta@syrmia.com>
> 
> This patch implements strace argument printing functionality for following 
> syscalls:
> 
>     *getxattr, lgetxattr, fgetxattr - retrieve an extended attribute value
> 
>         ssize_t getxattr(const char *path, const char *name, void *value, 
> size_t size)
>         ssize_t lgetxattr(const char *path, const char *name, void *value, 
> size_t size)
>         ssize_t fgetxattr(int fd, const char *name, void *value, size_t size)
>         man page: https://www.man7.org/linux/man-pages/man2/getxattr.2.html
> 
>     *listxattr, llistxattr, flistxattr - list extended attribute names
> 
>         ssize_t listxattr(const char *path, char *list, size_t size)
>         ssize_t llistxattr(const char *path, char *list, size_t size)
>         ssize_t flistxattr(int fd, char *list, size_t size)
>         man page: https://www.man7.org/linux/man-pages/man2/listxattr.2.html
> 
>     *removexattr, lremovexattr, fremovexattr - remove an extended attribute
> 
>          int removexattr(const char *path, const char *name)
>          int lremovexattr(const char *path, const char *name)
>          int fremovexattr(int fd, const char *name)
>          man page: 
> https://www.man7.org/linux/man-pages/man2/removexattr.2.html
> 
> Implementation notes:
> 
>     All of the syscalls have strings as argument types and thus a separate
>     printing function was stated in file "strace.list" for every one of them.
>     All of these printing functions were defined in "strace.c" using existing
>     printing functions for appropriate argument types:
>        "print_string()" - for (const char*) type
>        "print_pointer()" - for (char*) and (void *) type
>        "print_raw_param()" for (int) and (size_t) type
>     Syscalls "getxattr()" and "lgetxattr()" have the same number and type of
>     arguments and thus their print functions ("print_getxattr", 
> "print_lgetxattr")
>     share a same definition. The same statement applies to syscalls 
> "listxattr()"
>     and "llistxattr()".
>     Function "print_syscall_ret_listxattr()" was added to print the returned 
> list
>     of extended attributes for syscalls "print_listxattr(), 
> print_llistxattr() and
>     print_flistxattr()".
> 
> Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
> ---
>  linux-user/strace.c    | 122 +++++++++++++++++++++++++++++++++++++++++
>  linux-user/strace.list |  21 ++++---
>  2 files changed, 134 insertions(+), 9 deletions(-)
> 
> diff --git a/linux-user/strace.c b/linux-user/strace.c
> index 6d7accaa4c..f76bbbc1ff 100644
> --- a/linux-user/strace.c
> +++ b/linux-user/strace.c
> @@ -833,6 +833,41 @@ print_syscall_ret_adjtimex(const struct syscallname 
> *name, abi_long ret,
>  }
>  #endif
>  
> +#if defined(TARGET_NR_listxattr) || defined(TARGET_NR_llistxattr) \
> + || defined(TARGGET_NR_flistxattr)
> +static void
> +print_syscall_ret_listxattr(const struct syscallname *name, abi_long ret,
> +                            abi_long arg0, abi_long arg1, abi_long arg2,
> +                            abi_long arg3, abi_long arg4, abi_long arg5)
> +{
> +    print_syscall_err(ret);
> +
> +    if (ret >= 0) {
> +        qemu_log(TARGET_ABI_FMT_ld, ret);
> +        qemu_log(" (list = ");
> +        if (arg1 != 0) {
> +            abi_long bts_printed = 0;
> +            abi_long attr = arg1;
> +            while (bts_printed < ret) {

I don't think you need a new variable, you can do

               while (ret) {

> +                if (attr != arg1) {
> +                    qemu_log(",");
> +                }
> +                print_string(attr, 1);
> +                bts_printed += target_strlen(attr) + 1;

and
                   ret -= target_strlen(attr) + 1;

> +                attr += target_strlen(attr) + 1;
> +            }
> +        } else {
> +            qemu_log("NULL");
> +        }
> +        qemu_log(")");
> +    }
> +
> +    qemu_log("\n");
> +}
> +#define print_syscall_ret_llistxattr     print_syscall_ret_listxattr
> +#define print_syscall_ret_flistxattr     print_syscall_ret_listxattr
> +#endif
> +
>  UNUSED static struct flags access_flags[] = {
>      FLAG_GENERIC(F_OK),
>      FLAG_GENERIC(R_OK),

Thanks,
Laurent