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Use NtCreateFile directly in ReadLink

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This shaves off one syscall (we use one instead of two if we were to
use `windows.OpenFile` wrapper). Clean up flag generation in `OpenFile`.
Hopefully, we're in a much better place to *almost* support `openW`
and `openatW`.
This commit is contained in:
Jakub Konka 2020-07-30 23:00:25 +02:00
parent 8981b18fee
commit 390194431e
1 changed files with 56 additions and 19 deletions
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75
lib/std/os/windows.zig
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@ -56,10 +56,10 @@ pub const OpenFileOptions = struct {
/// TODO when share_access_nonblocking is false, this implementation uses
/// untinterruptible sleep() to block. This is not the final iteration of the API.
pub fn OpenFile(sub_path_w: []const u16, options: OpenFileOptions) OpenError!HANDLE {
if (mem.eql(u16, sub_path_w, &[_]u16{'.'}) and !options.open_dir and options.follow_symlinks) {
if (mem.eql(u16, sub_path_w, &[_]u16{'.'}) and !options.open_dir) {
return error.IsDir;
}
if (mem.eql(u16, sub_path_w, &[_]u16{ '.', '.' }) and !options.open_dir and options.follow_symlinks) {
if (mem.eql(u16, sub_path_w, &[_]u16{ '.', '.' }) and !options.open_dir) {
return error.IsDir;
}
@ -82,12 +82,13 @@ pub fn OpenFile(sub_path_w: []const u16, options: OpenFileOptions) OpenError!HAN
.SecurityQualityOfService = null,
};
var io: IO_STATUS_BLOCK = undefined;
const blocking_flag: ULONG = if (options.io_mode == .blocking) FILE_SYNCHRONOUS_IO_NONALERT else 0;
const file_or_dir_flag: ULONG = if (options.open_dir) FILE_DIRECTORY_FILE else FILE_NON_DIRECTORY_FILE;
// If we're not following symlinks, we need to ensure we don't pass in any synchronization flags such as FILE_SYNCHRONOUS_IO_NONALERT.
const flags: ULONG = if (options.follow_symlinks) file_or_dir_flag | blocking_flag else file_or_dir_flag | FILE_OPEN_REPARSE_POINT;
var delay: usize = 1;
while (true) {
const blocking_flag: ULONG = if (options.io_mode == .blocking) FILE_SYNCHRONOUS_IO_NONALERT else 0;
const file_or_dir_flag: ULONG = if (options.open_dir) FILE_DIRECTORY_FILE | FILE_OPEN_FOR_BACKUP_INTENT else FILE_NON_DIRECTORY_FILE;
const flags: ULONG = if (options.follow_symlinks) file_or_dir_flag | blocking_flag else FILE_OPEN_REPARSE_POINT;
const rc = ntdll.NtCreateFile(
&result,
options.access_mask,
@ -645,21 +646,57 @@ pub const ReadLinkError = error{
};
pub fn ReadLink(dir: ?HANDLE, sub_path_w: []const u16, out_buffer: []u8) ReadLinkError![]u8 {
const result_handle = OpenFile(sub_path_w, .{
.dir = dir,
.access_mask = FILE_READ_ATTRIBUTES,
.share_access = FILE_SHARE_READ,
.creation = FILE_OPEN,
.io_mode = .blocking,
.follow_symlinks = false,
}) catch |err| switch (err) {
error.WouldBlock => unreachable,
error.PipeBusy => unreachable,
error.IsDir => unreachable,
error.NoDevice => unreachable,
error.PathAlreadyExists => unreachable,
else => |e| return e,
// Here, we use `NtCreateFile` to shave off one syscall if we were to use `OpenFile` wrapper.
// With the latter, we'd need to call `NtCreateFile` twice, once for file symlink, and if that
// failed, again for dir symlink. Omitting any mention of file/dir flags makes it possible
// to open the symlink there and then.
const path_len_bytes = math.cast(u16, sub_path_w.len * 2) catch |err| switch (err) {
error.Overflow => return error.NameTooLong,
};
var nt_name = UNICODE_STRING{
.Length = path_len_bytes,
.MaximumLength = path_len_bytes,
.Buffer = @intToPtr([*]u16, @ptrToInt(sub_path_w.ptr)),
};
var attr = OBJECT_ATTRIBUTES{
.Length = @sizeOf(OBJECT_ATTRIBUTES),
.RootDirectory = if (std.fs.path.isAbsoluteWindowsWTF16(sub_path_w)) null else dir,
.Attributes = 0, // Note we do not use OBJ_CASE_INSENSITIVE here.
.ObjectName = &nt_name,
.SecurityDescriptor = null,
.SecurityQualityOfService = null,
};
var result_handle: HANDLE = undefined;
var io: IO_STATUS_BLOCK = undefined;
const rc = ntdll.NtCreateFile(
&result_handle,
FILE_READ_ATTRIBUTES,
&attr,
&io,
null,
FILE_ATTRIBUTE_NORMAL,
FILE_SHARE_READ,
FILE_OPEN,
FILE_OPEN_REPARSE_POINT,
null,
0,
);
switch (rc) {
.SUCCESS => {},
.OBJECT_NAME_INVALID => unreachable,
.OBJECT_NAME_NOT_FOUND => return error.FileNotFound,
.OBJECT_PATH_NOT_FOUND => return error.FileNotFound,
.NO_MEDIA_IN_DEVICE => return error.FileNotFound,
.INVALID_PARAMETER => unreachable,
.SHARING_VIOLATION => return error.AccessDenied,
.ACCESS_DENIED => return error.AccessDenied,
.PIPE_BUSY => return error.AccessDenied,
.OBJECT_PATH_SYNTAX_BAD => unreachable,
.OBJECT_NAME_COLLISION => unreachable,
.FILE_IS_A_DIRECTORY => unreachable,
else => return unexpectedStatus(rc),
}
defer CloseHandle(result_handle);
var reparse_buf: [MAXIMUM_REPARSE_DATA_BUFFER_SIZE]u8 = undefined;