[PATCH 4/9] bsd-user: Two helper routines oidfmt and sysctl_oldcvt

[Warner Losh <imp@bsdimp.com>]

From: Stacey Son <sson@FreeBSD.org>

oidfmt uses undocumented system call to get the type of the sysctl.
sysctl_oldcvt does the byte swapping in the data to return it to the
target.

Co-Authored-by: Sean Bruno <sbruno@FreeBSD.org>
Signed-off-by: Sean Bruno <sbruno@FreeBSD.org>
Co-Authored-by: Juergen Lock <nox@jelal.kn-bremen.de>
Signed-off-by: Juergen Lock <nox@jelal.kn-bremen.de>
Co-Authored-by: Raphael Kubo da Costa <rakuco@FreeBSD.org>
Signed-off-by: Raphael Kubo da Costa <rakuco@FreeBSD.org>
Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
---
 bsd-user/freebsd/os-sys.c | 94 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)

diff --git a/bsd-user/freebsd/os-sys.c b/bsd-user/freebsd/os-sys.c
index 1676ec10f83..e3b9f168a2b 100644
--- a/bsd-user/freebsd/os-sys.c
+++ b/bsd-user/freebsd/os-sys.c
@@ -21,6 +21,100 @@
 #include "qemu.h"
 #include "target_arch_sysarch.h"
 
+#include <sys/sysctl.h>
+
+/*
+ * This uses the undocumented oidfmt interface to find the kind of a requested
+ * sysctl, see /sys/kern/kern_sysctl.c:sysctl_sysctl_oidfmt() (compare to
+ * src/sbin/sysctl/sysctl.c)
+ */
+static int oidfmt(int *oid, int len, char *fmt, uint32_t *kind)
+{
+    int qoid[CTL_MAXNAME + 2];
+    uint8_t buf[BUFSIZ];
+    int i;
+    size_t j;
+
+    qoid[0] = 0;
+    qoid[1] = 4;
+    memcpy(qoid + 2, oid, len * sizeof(int));
+
+    j = sizeof(buf);
+    i = sysctl(qoid, len + 2, buf, &j, 0, 0);
+    if (i) {
+        return i;
+    }
+
+    if (kind) {
+        *kind = *(uint32_t *)buf;
+    }
+
+    if (fmt) {
+        strcpy(fmt, (char *)(buf + sizeof(uint32_t)));
+    }
+    return 0;
+}
+
+/*
+ * try and convert sysctl return data for the target.
+ * Note: doesn't handle CTLTYPE_OPAQUE and CTLTYPE_STRUCT.
+ */
+static int sysctl_oldcvt(void *holdp, size_t *holdlen, uint32_t kind)
+{
+    switch (kind & CTLTYPE) {
+    case CTLTYPE_INT:
+    case CTLTYPE_UINT:
+        *(uint32_t *)holdp = tswap32(*(uint32_t *)holdp);
+        break;
+
+#ifdef TARGET_ABI32
+    case CTLTYPE_LONG:
+    case CTLTYPE_ULONG:
+        /*
+         * If the sysctl has a type of long/ulong but seems to be bigger than
+         * these data types, its probably an array.  Double check that its
+         * evenly divisible by the size of long and convert holdp to a series of
+         * 32bit elements instead, adjusting holdlen to the new size.
+         */
+        if ((*holdlen > sizeof(abi_ulong)) &&
+            ((*holdlen % sizeof(abi_ulong)) == 0)) {
+            int array_size = *holdlen / sizeof(long);
+            int i;
+            if (holdp) {
+                for (i = 0; i < array_size; i++) {
+                    ((uint32_t *)holdp)[i] = tswap32(((long *)holdp)[i]);
+                }
+                *holdlen = array_size * sizeof(abi_ulong);
+            } else {
+                *holdlen = sizeof(abi_ulong);
+            }
+        } else {
+            *(uint32_t *)holdp = tswap32(*(long *)holdp);
+            *holdlen = sizeof(uint32_t);
+        }
+        break;
+#else
+    case CTLTYPE_LONG:
+        *(uint64_t *)holdp = tswap64(*(long *)holdp);
+        break;
+    case CTLTYPE_ULONG:
+        *(uint64_t *)holdp = tswap64(*(unsigned long *)holdp);
+        break;
+#endif
+    case CTLTYPE_U64:
+    case CTLTYPE_S64:
+        *(uint64_t *)holdp = tswap64(*(uint64_t *)holdp);
+        break;
+
+    case CTLTYPE_STRING:
+        break;
+
+    default:
+        return -1;
+    }
+    return 0;
+}
+
 /* sysarch() is architecture dependent. */
 abi_long do_freebsd_sysarch(void *cpu_env, abi_long arg1, abi_long arg2)
 {
-- 
2.39.1