Re: [Qemu-devel] [PATCH v3] linux-user: add signalfd/signalfd4 syscalls

[Riku Voipio]

Hi,

On Mon, Sep 28, 2015 at 11:42:28PM +0200, Laurent Vivier wrote:
> This patch introduces a system very similar to the one used in the kernel
> to attach specific functions to a given file descriptor.
> 
> In this case, we attach a specific "host_to_target()" translator to the fd
> returned by signalfd() to be able to byte-swap the signalfd_siginfo
> structure provided by read().
> 
> This patch allows to execute the example program given by
> man signalfd(2):

Looks good, but unfortunately collides with your 
name_to_handle_at/open_by_handle_at
patch. Can you update in on top of that patch, or better, agains the que
at:

https://git.linaro.org/people/riku.voipio/qemu.git/shortlog/refs/heads/linux-user-for-upstream

I take this means adding fd_trans_unregister to the open_by_handle_at
function.

>  #include <sys/signalfd.h>
>  #include <signal.h>
>  #include <unistd.h>
>  #include <stdlib.h>
>  #include <stdio.h>
> 
>  #define handle_error(msg) \
>      do { perror(msg); exit(EXIT_FAILURE); } while (0)
> 
>  int
>  main(int argc, char *argv[])
>  {
>      sigset_t mask;
>      int sfd;
>      struct signalfd_siginfo fdsi;
>      ssize_t s;
> 
>      sigemptyset(&mask);
>      sigaddset(&mask, SIGINT);
>      sigaddset(&mask, SIGQUIT);
> 
>      /* Block signals so that they aren't handled
>         according to their default dispositions */
> 
>      if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)
>          handle_error("sigprocmask");
> 
>      sfd = signalfd(-1, &mask, 0);
>      if (sfd == -1)
>          handle_error("signalfd");
> 
>      for (;;) {
>          s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
>          if (s != sizeof(struct signalfd_siginfo))
>              handle_error("read");
> 
>          if (fdsi.ssi_signo == SIGINT) {
>              printf("Got SIGINT\n");
>          } else if (fdsi.ssi_signo == SIGQUIT) {
>              printf("Got SIGQUIT\n");
>              exit(EXIT_SUCCESS);
>          } else {
>              printf("Read unexpected signal\n");
>          }
>      }
>  }
> 
>  $ ./signalfd_demo
>  ^CGot SIGINT
>  ^CGot SIGINT
>  ^\Got SIGQUIT
> 
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
> v3: Combine struct definition and typedef
>     replace a = x ? y : z by if () { }
>     clear extra memory from g_realloc()
>     remove useless management of O_CLOEXEC
>     swap ssi_addr_lsb
>     fix host_flags checking
> v2: Update commit message with example from man page
>     Use CamelCase for struct
>     Allocate entries in the fd array on demand
>     Clear fd entries on open(), close(),...
>     Swap ssi_errno
>     Try to manage dup() and O_CLOEXEC cases
>     Fix signalfd() parameters
>     merge signalfd() and signalfd4()
>     Change the API to only provide functions to process
>     data stream.
> 
>     TargetFdTrans has an unused field, target_to_host, for symmetry
>     and which could used later with netlink() functions.
> 
>  linux-user/syscall.c | 165 
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 165 insertions(+)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index f62c698..b22b9f4 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -60,6 +60,7 @@ int __clone2(int (*fn)(void *), void *child_stack_base,
>  #include <sys/statfs.h>
>  #include <utime.h>
>  #include <sys/sysinfo.h>
> +#include <sys/signalfd.h>
>  //#include <sys/user.h>
>  #include <netinet/ip.h>
>  #include <netinet/tcp.h>
> @@ -294,6 +295,54 @@ static bitmask_transtbl fcntl_flags_tbl[] = {
>    { 0, 0, 0, 0 }
>  };
>  
> +typedef abi_long (*TargetFdFunc)(void *, size_t);
> +typedef struct TargetFdTrans {
> +    TargetFdFunc host_to_target;
> +    TargetFdFunc target_to_host;
> +} TargetFdTrans;
> +
> +static TargetFdTrans **target_fd_trans;
> +
> +static unsigned int target_fd_max;
> +
> +static TargetFdFunc fd_trans_host_to_target(int fd)
> +{
> +    if (fd < target_fd_max && target_fd_trans[fd]) {
> +        return target_fd_trans[fd]->host_to_target;
> +    }
> +    return NULL;
> +}
> +
> +static void fd_trans_register(int fd, TargetFdTrans *trans)
> +{
> +    unsigned int oldmax;
> +
> +    if (fd >= target_fd_max) {
> +        oldmax = target_fd_max;
> +        target_fd_max = ((fd >> 6) + 1) << 6; /* by slice of 64 entries */
> +        target_fd_trans = g_realloc(target_fd_trans,
> +                                    target_fd_max * sizeof(TargetFdTrans));
> +        memset((void *)(target_fd_trans + oldmax), 0,
> +               (target_fd_max - oldmax) * sizeof(TargetFdTrans *));
> +    }
> +    target_fd_trans[fd] = trans;
> +}
> +
> +static void fd_trans_unregister(int fd)
> +{
> +    if (fd >= 0 && fd < target_fd_max) {
> +        target_fd_trans[fd] = NULL;
> +    }
> +}
> +
> +static void fd_trans_dup(int oldfd, int newfd)
> +{
> +    fd_trans_unregister(newfd);
> +    if (oldfd < target_fd_max && target_fd_trans[oldfd]) {
> +        fd_trans_register(newfd, target_fd_trans[oldfd]);
> +    }
> +}
> +
>  static int sys_getcwd1(char *buf, size_t size)
>  {
>    if (getcwd(buf, size) == NULL) {
> @@ -5246,6 +5295,91 @@ static int do_futex(target_ulong uaddr, int op, int 
> val, target_ulong timeout,
>          return -TARGET_ENOSYS;
>      }
>  }
> +#if defined(TARGET_NR_signalfd) || defined(TARGET_NR_signalfd4)
> +
> +/* signalfd siginfo conversion */
> +
> +static void
> +host_to_target_signalfd_siginfo(struct signalfd_siginfo *tinfo,
> +                                const struct signalfd_siginfo *info)
> +{
> +    int sig = host_to_target_signal(info->ssi_signo);
> +
> +    /* linux/signalfd.h defines a ssi_addr_lsb
> +     * not defined in sys/signalfd.h but used by some kernels
> +     */
> +
> +#ifdef BUS_MCEERR_AO
> +    if (tinfo->ssi_signo == SIGBUS &&
> +        (tinfo->ssi_code == BUS_MCEERR_AR ||
> +         tinfo->ssi_code == BUS_MCEERR_AO)) {
> +        uint16_t *ssi_addr_lsb = (uint16_t *)(&info->ssi_addr + 1);
> +        uint16_t *tssi_addr_lsb = (uint16_t *)(&tinfo->ssi_addr + 1);
> +        *tssi_addr_lsb = tswap16(*ssi_addr_lsb);
> +    }
> +#endif
> +
> +    tinfo->ssi_signo = tswap32(sig);
> +    tinfo->ssi_errno = tswap32(tinfo->ssi_errno);
> +    tinfo->ssi_code = tswap32(info->ssi_code);
> +    tinfo->ssi_pid = tswap32(info->ssi_pid);
> +    tinfo->ssi_uid = tswap32(info->ssi_uid);
> +    tinfo->ssi_fd = tswap32(info->ssi_fd);
> +    tinfo->ssi_tid = tswap32(info->ssi_tid);
> +    tinfo->ssi_band = tswap32(info->ssi_band);
> +    tinfo->ssi_overrun = tswap32(info->ssi_overrun);
> +    tinfo->ssi_trapno = tswap32(info->ssi_trapno);
> +    tinfo->ssi_status = tswap32(info->ssi_status);
> +    tinfo->ssi_int = tswap32(info->ssi_int);
> +    tinfo->ssi_ptr = tswap64(info->ssi_ptr);
> +    tinfo->ssi_utime = tswap64(info->ssi_utime);
> +    tinfo->ssi_stime = tswap64(info->ssi_stime);
> +    tinfo->ssi_addr = tswap64(info->ssi_addr);
> +}
> +
> +static abi_long host_to_target_signalfd(void *buf, size_t len)
> +{
> +    int i;
> +
> +    for (i = 0; i < len; i += sizeof(struct signalfd_siginfo)) {
> +        host_to_target_signalfd_siginfo(buf + i, buf + i);
> +    }
> +
> +    return len;
> +}
> +
> +static TargetFdTrans target_signalfd_trans = {
> +    .host_to_target = host_to_target_signalfd,
> +};
> +
> +static abi_long do_signalfd4(int fd, abi_long mask, int flags)
> +{
> +    int host_flags;
> +    target_sigset_t *target_mask;
> +    sigset_t host_mask;
> +    abi_long ret;
> +
> +    if (flags & ~(TARGET_O_NONBLOCK | TARGET_O_CLOEXEC)) {
> +        return -TARGET_EINVAL;
> +    }
> +    if (!lock_user_struct(VERIFY_READ, target_mask, mask, 1)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    target_to_host_sigset(&host_mask, target_mask);
> +
> +    host_flags = target_to_host_bitmask(flags, fcntl_flags_tbl);
> +
> +    ret = get_errno(signalfd(fd, &host_mask, host_flags));
> +    if (ret >= 0) {
> +        fd_trans_register(ret, &target_signalfd_trans);
> +    }
> +
> +    unlock_user_struct(target_mask, mask, 0);
> +
> +    return ret;
> +}
> +#endif
>  
>  /* Map host to target signal numbers for the wait family of syscalls.
>     Assume all other status bits are the same.  */
> @@ -5630,6 +5764,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>              if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
>                  goto efault;
>              ret = get_errno(read(arg1, p, arg3));
> +            if (ret >= 0 &&
> +                fd_trans_host_to_target(arg1)) {
> +                ret = fd_trans_host_to_target(arg1)(p, ret);
> +            }
>              unlock_user(p, arg2, ret);
>          }
>          break;
> @@ -5645,6 +5783,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          ret = get_errno(do_openat(cpu_env, AT_FDCWD, p,
>                                    target_to_host_bitmask(arg2, 
> fcntl_flags_tbl),
>                                    arg3));
> +        fd_trans_unregister(ret);
>          unlock_user(p, arg1, 0);
>          break;
>      case TARGET_NR_openat:
> @@ -5653,9 +5792,11 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          ret = get_errno(do_openat(cpu_env, arg1, p,
>                                    target_to_host_bitmask(arg3, 
> fcntl_flags_tbl),
>                                    arg4));
> +        fd_trans_unregister(ret);
>          unlock_user(p, arg2, 0);
>          break;
>      case TARGET_NR_close:
> +        fd_trans_unregister(arg1);
>          ret = get_errno(close(arg1));
>          break;
>      case TARGET_NR_brk:
> @@ -5695,6 +5836,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          if (!(p = lock_user_string(arg1)))
>              goto efault;
>          ret = get_errno(creat(p, arg2));
> +        fd_trans_unregister(ret);
>          unlock_user(p, arg1, 0);
>          break;
>  #endif
> @@ -6130,6 +6272,9 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          break;
>      case TARGET_NR_dup:
>          ret = get_errno(dup(arg1));
> +        if (ret >= 0) {
> +            fd_trans_dup(arg1, ret);
> +        }
>          break;
>      case TARGET_NR_pipe:
>          ret = do_pipe(cpu_env, arg1, 0, 0);
> @@ -6222,10 +6367,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          goto unimplemented;
>      case TARGET_NR_dup2:
>          ret = get_errno(dup2(arg1, arg2));
> +        if (ret >= 0) {
> +            fd_trans_dup(arg1, arg2);
> +        }
>          break;
>  #if defined(CONFIG_DUP3) && defined(TARGET_NR_dup3)
>      case TARGET_NR_dup3:
>          ret = get_errno(dup3(arg1, arg2, arg3));
> +        if (ret >= 0) {
> +            fd_trans_dup(arg1, arg2);
> +        }
>          break;
>  #endif
>  #ifdef TARGET_NR_getppid /* not on alpha */
> @@ -7215,6 +7366,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>  #ifdef TARGET_NR_socket
>      case TARGET_NR_socket:
>          ret = do_socket(arg1, arg2, arg3);
> +        fd_trans_unregister(ret);
>          break;
>  #endif
>  #ifdef TARGET_NR_socketpair
> @@ -9454,6 +9606,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>  #if defined(TARGET_NR_eventfd)
>      case TARGET_NR_eventfd:
>          ret = get_errno(eventfd(arg1, 0));
> +        fd_trans_unregister(ret);
>          break;
>  #endif
>  #if defined(TARGET_NR_eventfd2)
> @@ -9467,6 +9620,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>              host_flags |= O_CLOEXEC;
>          }
>          ret = get_errno(eventfd(arg1, host_flags));
> +        fd_trans_unregister(ret);
>          break;
>      }
>  #endif
> @@ -9509,6 +9663,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          break;
>  #endif
>  #endif
> +#if defined(TARGET_NR_signalfd4)
> +    case TARGET_NR_signalfd4:
> +        ret = do_signalfd4(arg1, arg2, arg4);
> +        break;
> +#endif
> +#if defined(TARGET_NR_signalfd)
> +    case TARGET_NR_signalfd:
> +        ret = do_signalfd4(arg1, arg2, 0);
> +        break;
> +#endif
>  #if defined(CONFIG_EPOLL)
>  #if defined(TARGET_NR_epoll_create)
>      case TARGET_NR_epoll_create:
> @@ -9780,6 +9944,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>              timer_t htimer = g_posix_timers[timerid];
>              ret = get_errno(timer_getoverrun(htimer));
>          }
> +        fd_trans_unregister(ret);
>          break;
>      }
>  #endif
> -- 
> 2.4.3
> 
>