Linux: Add cachestat, fchmodat2 syscalls (#958)

libc/calls/cachestat.c

@@ -0,0 +1,47 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+
+#include "libc/calls/cachestat.h"
+#include "libc/intrin/strace.internal.h"
+
+int sys_cachestat(int, struct cachestat_range *, struct cachestat *, uint32_t);
+
+/**
+ * Query the page cache statistics of a file.
+ *
+ * @param fd The open file descriptor to retrieve statistics from.
+ * @param cstat_range The byte range in `fd` to query. When `len > 0`, the range
+ * is `[off..off + len]`. When `len` == 0, the range is from `off` to the end of
+ * `fd`.
+ * @param cstat The structure where page cache statistics are stored.
+ * @param flags Currently unused, and must be set to `0`.
+ * @return 0 on success, or -1 w/ errno.
+ * @raise EFAULT if `cstat_range` or `cstat` points to invalid memory
+ * @raise EINVAL if `flags` is nonzero
+ * @raise EBADF  if `fd` is negative or not open
+ * @raise EOPNOTSUPP if `fd` refers to a hugetlbfs file
+ * @raise ENOSYS if not Linux 6.5
+ */
+int cachestat(int fd, struct cachestat_range *cstat_range,
+              struct cachestat *cstat, uint32_t flags) {
+  int rc;
+  rc = sys_cachestat(fd, cstat_range, cstat, flags);
+  STRACE("cachestat(%d, %p, %p, %#x) → %d% m", fd, cstat_range, cstat, flags);
+  return rc;
+}