Add file_open(): the underlying system call of openat().

CloudABI purely operates on file descriptor rights (CAP_*). File
descriptor access modes (O_ACCMODE) are emulated on top of rights.

Instead of accepting the traditional flags argument, file_open() copies
in an fdstat_t object that contains the initial rights the descriptor
should have, but also file descriptor flags that should persist after
opening (APPEND, NONBLOCK, *SYNC). Only flags that don't persist (EXCL,
TRUNC, CREAT, DIRECTORY) are passed in as an argument.

file_open() first converts the rights, the persistent flags and the
non-persistent flags to fflags. It then calls into vn_open(). If
successful, it installs the file descriptor with the requested
rights, trimming off rights that don't apply to the type of
the file that has been opened.

Unlike kern_openat(), this function does not support /dev/fd/*. I can't
think of a reason why we need to support this for CloudABI.

Obtained from:	https://github.com/NuxiNL/freebsd
Differential Revision:	https://reviews.freebsd.org/D3235

1 files changed, 20 insertions, 1 deletions

diff --git a/sys/compat/cloudabi/cloudabi_fd.c b/sys/compat/cloudabi/cloudabi_fd.c
index 1fed2e7dcf4f..f16d66855ad4 100644
--- a/sys/compat/cloudabi/cloudabi_fd.c
+++ b/sys/compat/cloudabi/cloudabi_fd.c
@@ -290,7 +290,7 @@ cloudabi_convert_filetype(const struct file *fp)
 }
 
 /* Removes rights that conflict with the file descriptor type. */
-static void
+void
 cloudabi_remove_conflicting_rights(cloudabi_filetype_t filetype,
     cloudabi_rights_t *base, cloudabi_rights_t *inheriting)
 {
@@ -499,6 +499,25 @@ cloudabi_sys_fd_stat_get(struct thread *td,
 	return (copyout(&fsb, (void *)uap->buf, sizeof(fsb)));
 }
 
+/* Converts CloudABI rights to a set of Capsicum capabilities. */
+int
+cloudabi_convert_rights(cloudabi_rights_t in, cap_rights_t *out)
+{
+
+	cap_rights_init(out);
+#define MAPPING(cloudabi, ...) do {			\
+	if (in & (cloudabi)) {				\
+		cap_rights_set(out, ##__VA_ARGS__);	\
+		in &= ~(cloudabi);			\
+	}						\
+} while (0);
+	RIGHTS_MAPPINGS
+#undef MAPPING
+	if (in != 0)
+		return (ENOTCAPABLE);
+	return (0);
+}
+
 int
 cloudabi_sys_fd_stat_put(struct thread *td,
     struct cloudabi_sys_fd_stat_put_args *uap)