syscalls: pread and pwrite

kernel-src/sys/syscalls/pwrite.c

@@ -0,0 +1,54 @@
+#include <kernel/syscalls.h>
+#include <kernel/vfs.h>
+#include <kernel/file.h>
+#include <errno.h>
+
+syscallret_t syscall_pwrite(context_t *context, int fd, void *buffer, size_t size, uintmax_t offset) {
+	syscallret_t ret = {
+		.ret = -1
+	};
+
+	void *kernelbuff = vmm_map(NULL, size, VMM_FLAGS_ALLOCATE, ARCH_MMU_FLAGS_READ | ARCH_MMU_FLAGS_WRITE | ARCH_MMU_FLAGS_NOEXEC, NULL);
+	if (kernelbuff == NULL) {
+		ret.errno = ENOMEM;
+		return ret;
+	}
+
+	file_t *file = fd_get(fd);
+
+	if (file == NULL || (file->flags & FILE_WRITE) == 0) {
+		ret.errno = EBADF;
+		goto cleanup;
+	}
+
+	if (size == 0) {
+		ret.ret = 0;
+		ret.errno = 0;
+		goto cleanup;
+	}
+
+	ret.errno = usercopy_fromuser(kernelbuff, buffer, size);
+	if (ret.errno)
+		goto cleanup;
+
+	size_t tmp;
+	if (file->vnode->type == V_TYPE_SOCKET || file->vnode->type == V_TYPE_FIFO || (file->vnode->type == V_TYPE_CHDEV && VOP_MAXSEEK(file->vnode, &tmp))) {
+		ret.errno = ESPIPE;
+		goto cleanup;
+	}
+
+	size_t byteswritten;
+	ret.errno = vfs_write(file->vnode, kernelbuff, size, offset, &byteswritten, fileflagstovnodeflags(file->flags));
+
+	if (ret.errno)
+		goto cleanup;
+
+	ret.ret = byteswritten;
+	ret.errno = 0;
+cleanup:
+	if (file)
+		fd_release(file);
+
+	vmm_unmap(kernelbuff, size, 0);
+	return ret;
+}