9pfs: Add FreeBSD support

This is largely derived from existing Darwin support.  FreeBSD
apparently has better support for *at() system calls so doesn't require
workarounds for a missing mknodat().  The implementation has a couple of
warts however:
- The extattr(2) system calls don't support anything akin to
  XATTR_CREATE or XATTR_REPLACE, so a racy workaround is implemented.
- Attribute names cannot begin with "user." or "system." on ZFS.
  However FreeBSD's extattr(2) system calls support two dedicated
  namespaces for these two.  So "user." or "system." prefixes are
  trimmed off from attribute names and instead EXTATTR_NAMESPACE_USER or
  EXTATTR_NAMESPACE_SYSTEM are picked and passed to extattr system calls
  accordingly.

The 9pfs tests were verified to pass on the UFS, ZFS and tmpfs
filesystems.

Signed-off-by: Mark Johnston <markj@FreeBSD.org>
Link: https://lore.kernel.org/qemu-devel/aJOWhHB2p-fbueAm@nuc
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

1 files changed, 132 insertions, 0 deletions

diff --git a/hw/9pfs/9p-util-freebsd.c b/hw/9pfs/9p-util-freebsd.c
new file mode 100644
index 0000000000..9dd1d069f6
--- /dev/null
+++ b/hw/9pfs/9p-util-freebsd.c
@@ -0,0 +1,132 @@
+/*
+ * 9p utilities (FreeBSD Implementation)
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/xattr.h"
+#include "9p-util.h"
+
+static int mangle_xattr_name(const char **namep)
+{
+    const char *name = *namep;
+
+    /*
+     * ZFS forbids attributes in starting with "user." or "system.".
+     */
+    if (strncmp(name, "system.", 7) == 0) {
+        *namep = name + 7;
+        return EXTATTR_NAMESPACE_SYSTEM;
+    }
+    if (strncmp(name, "user.", 5) == 0) {
+        *namep = name + 5;
+    }
+    return EXTATTR_NAMESPACE_USER;
+}
+
+ssize_t fgetxattr(int fd, const char *name, void *value, size_t size)
+{
+    int namespace;
+
+    namespace = mangle_xattr_name(&name);
+    return extattr_get_fd(fd, namespace, name, value, size);
+}
+
+ssize_t fgetxattrat_nofollow(int dirfd, const char *filename, const char *name,
+                             void *value, size_t size)
+{
+    ssize_t ret;
+    int fd, namespace;
+
+    fd = openat_file(dirfd, filename,
+                     O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
+    if (fd == -1) {
+        return -1;
+    }
+    namespace = mangle_xattr_name(&name);
+    ret = extattr_get_fd(fd, namespace, name, value, size);
+    close_preserve_errno(fd);
+    return ret;
+}
+
+ssize_t flistxattrat_nofollow(int dirfd, const char *filename,
+                              char *list, size_t size)
+{
+    ssize_t ret;
+    int fd;
+
+    fd = openat_file(dirfd, filename,
+                     O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
+    if (fd == -1) {
+        return -1;
+    }
+    ret = extattr_list_fd(fd, EXTATTR_NAMESPACE_USER, list, size);
+    close_preserve_errno(fd);
+    return ret;
+}
+
+ssize_t fremovexattrat_nofollow(int dirfd, const char *filename,
+                                const char *name)
+{
+    int fd, namespace, ret;
+
+    fd = openat_file(dirfd, filename,
+                     O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
+    if (fd == -1) {
+        return -1;
+    }
+    namespace = mangle_xattr_name(&name);
+    ret = extattr_delete_fd(fd, namespace, name);
+    close_preserve_errno(fd);
+    return ret;
+}
+
+int fsetxattrat_nofollow(int dirfd, const char *filename, const char *name,
+                         void *value, size_t size, int flags)
+{
+    ssize_t ret;
+    int fd, namespace;
+
+    namespace = mangle_xattr_name(&name);
+    if (flags == (XATTR_CREATE | XATTR_REPLACE)) {
+        errno = EINVAL;
+        return -1;
+    }
+    fd = openat_file(dirfd, filename,
+                     O_RDONLY | O_PATH_9P_UTIL | O_NOFOLLOW, 0);
+    if (fd == -1) {
+        return -1;
+    }
+    if (flags & (XATTR_CREATE | XATTR_REPLACE)) {
+        ret = extattr_get_fd(fd, namespace, name, NULL, 0);
+        if (ret == -1 && errno != ENOATTR) {
+            close_preserve_errno(fd);
+            return -1;
+        }
+        if (ret >= 0 && (flags & XATTR_CREATE)) {
+            errno = EEXIST;
+            close_preserve_errno(fd);
+            return -1;
+        }
+        if (ret == -1 && (flags & XATTR_REPLACE)) {
+            errno = ENOATTR;
+            close_preserve_errno(fd);
+            return -1;
+        }
+    }
+    ret = extattr_set_fd(fd, namespace, name, value, size);
+    close_preserve_errno(fd);
+    return ret;
+}
+
+int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
+{
+    return mknodat(dirfd, filename, mode, dev);
+}