Re: [PATCH v2 2/4] tools: Import standalone sd_notify() implementation from systemd

[Jürgen Groß <jgross@xxxxxxxx>]

On 16.05.24 20:58, Andrew Cooper wrote:
> ... in order to avoid linking against the whole of libsystemd.
>
> Only minimal changes to the upstream copy, to function as a drop-in
> replacement for sd_notify() and as a header-only library.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
With s/cleanup(sd_closep)/cleanup(xen_sd_closep)/

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

> ---
> CC: Anthony PERARD <anthony@xxxxxxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: George Dunlap <George.Dunlap@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Christian Lindig <christian.lindig@xxxxxxxxxx>
> CC: Edwin Török <edwin.torok@xxxxxxxxx>
>
> v2:
>   * New
> ---
>   tools/include/xen-sd-notify.h | 98 +++++++++++++++++++++++++++++++++++
>   1 file changed, 98 insertions(+)
>   create mode 100644 tools/include/xen-sd-notify.h
>
> diff --git a/tools/include/xen-sd-notify.h b/tools/include/xen-sd-notify.h
> new file mode 100644
> index 000000000000..eda9d8b22d9e
> --- /dev/null
> +++ b/tools/include/xen-sd-notify.h
> @@ -0,0 +1,98 @@
> +/* SPDX-License-Identifier: MIT-0 */
> +
> +/*
> + * Implement the systemd notify protocol without external dependencies.
> + * Supports both readiness notification on startup and on reloading,
> + * according to the protocol defined at:
> + * https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
> + * This protocol is guaranteed to be stable as per:
> + * https://systemd.io/PORTABILITY_AND_STABILITY/
> + *
> + * Differences from the upstream copy:
> + * - Rename/rework as a drop-in replacement for systemd/sd-daemon.h
> + * - Only take the subset Xen cares about
> + * - Respect -Wdeclaration-after-statement
> + */
> +
> +#ifndef XEN_SD_NOTIFY
> +#define XEN_SD_NOTIFY
> +
> +#include <errno.h>
> +#include <stddef.h>
> +#include <stdlib.h>
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <unistd.h>
> +
> +static inline void xen_sd_closep(int *fd) {
> +  if (!fd || *fd < 0)
> +    return;
> +
> +  close(*fd);
> +  *fd = -1;
> +}
> +
> +static inline int xen_sd_notify(const char *message) {
> +  union sockaddr_union {
> +    struct sockaddr sa;
> +    struct sockaddr_un sun;
> +  } socket_addr = {
> +    .sun.sun_family = AF_UNIX,
> +  };
> +  size_t path_length, message_length;
> +  ssize_t written;
> +  const char *socket_path;
> +  int __attribute__((cleanup(sd_closep))) fd = -1;
> +
> +  /* Verify the argument first */
> +  if (!message)
> +    return -EINVAL;
> +
> +  message_length = strlen(message);
> +  if (message_length == 0)
> +    return -EINVAL;
> +
> +  /* If the variable is not set, the protocol is a noop */
> +  socket_path = getenv("NOTIFY_SOCKET");
> +  if (!socket_path)
> +    return 0; /* Not set? Nothing to do */
> +
> +  /* Only AF_UNIX is supported, with path or abstract sockets */
> +  if (socket_path[0] != '/' && socket_path[0] != '@')
> +    return -EAFNOSUPPORT;
> +
> +  path_length = strlen(socket_path);
> +  /* Ensure there is room for NUL byte */
> +  if (path_length >= sizeof(socket_addr.sun.sun_path))
> +    return -E2BIG;
> +
> +  memcpy(socket_addr.sun.sun_path, socket_path, path_length);
> +
> +  /* Support for abstract socket */
> +  if (socket_addr.sun.sun_path[0] == '@')
> +    socket_addr.sun.sun_path[0] = 0;
> +
> +  fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
> +  if (fd < 0)
> +    return -errno;
> +
> +  if (connect(fd, &socket_addr.sa, offsetof(struct sockaddr_un, sun_path) + 
> path_length) != 0)
> +    return -errno;
> +
> +  written = write(fd, message, message_length);
> +  if (written != (ssize_t) message_length)
> +    return written < 0 ? -errno : -EPROTO;
> +
> +  return 1; /* Notified! */
> +}
> +
> +static inline int sd_notify(int unset_environment, const char *message) {
> +    int r = xen_sd_notify(message);
> +
> +    if (unset_environment)
> +        unsetenv("NOTIFY_SOCKET");
> +
> +    return r;
> +}
> +
> +#endif /* XEN_SD_NOTIFY */