Re: [PATCH v3 3/6] linux-user: Add strace support for printing argument of syscalls used for extended attributes

[Laurent Vivier <laurent@vivier.eu>]

Le 11/06/2020 à 17:51, 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

Compared to v2, fremovexattr, removexattr and lremovexattr are missing.

> 
> 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    | 95 ++++++++++++++++++++++++++++++++++++++++++
>  linux-user/strace.list | 15 ++++---
>  2 files changed, 104 insertions(+), 6 deletions(-)
> 
> diff --git a/linux-user/strace.c b/linux-user/strace.c
> index 4f85606c19..a7c3ea8df3 100644
> --- a/linux-user/strace.c
> +++ b/linux-user/strace.c
> @@ -834,6 +834,41 @@ 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)
> +{
> +    const char *errstr = NULL;
> +
> +    SYSCALL_RET_ERR(ret, errstr);
> +
> +    if (ret >= 0) {
> +        qemu_log(TARGET_ABI_FMT_ld, ret);
> +        qemu_log(" (list = ");
> +        if (arg1 != 0) {
> +            abi_long attr = arg1;
> +            while (target_strlen(attr) != 0) {

You can't rely on target_strlen(), you should rely on the value returned
by the ioctl() (ret) that is defined as the length of the returned data.

Thanks,
Laurent