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std.os.windows.GetFinalPathNameByHandle: remove intermediate buffers

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... and mem.copy operations. Requires slightly larger input buffers than result length. Add helper functions std.mem.alignInBytes and std.mem.alignInSlice.
This commit is contained in:
Rohlem
2020-12-23 22:10:28 +01:00
committed by Andrew Kelley
parent f301a8467c
commit c96272f618
2 changed files with 67 additions and 27 deletions
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43
lib/std/mem.zig
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@@ -2436,3 +2436,46 @@ test "freeing empty string with null-terminated sentinel" {
const empty_string = try dupeZ(testing.allocator, u8, "");
testing.allocator.free(empty_string);
}
/// Returns a slice with the given new alignment,
/// all other pointer attributes copied from `AttributeSource`.
fn AlignedSlice(comptime AttributeSource: type, comptime new_alignment: u29) type {
const info = @typeInfo(AttributeSource).Pointer;
return @Type(.{
.Pointer = .{
.size = .Slice,
.is_const = info.is_const,
.is_volatile = info.is_volatile,
.is_allowzero = info.is_allowzero,
.alignment = new_alignment,
.child = info.child,
.sentinel = null,
},
});
}
/// Returns the largest slice in the given bytes that conforms to the new alignment,
/// or `null` if the given bytes contain no conforming address.
pub fn alignInBytes(bytes: []u8, comptime new_alignment: usize) ?[]align(new_alignment) u8 {
const begin_address = @ptrToInt(bytes.ptr);
const end_address = begin_address + bytes.len;
const begin_address_aligned = mem.alignForward(begin_address, new_alignment);
const new_length = std.math.sub(usize, end_address, begin_address_aligned) catch |e| switch (e) {
error.Overflow => return null,
};
const alignment_offset = begin_address_aligned - begin_address;
return @alignCast(new_alignment, bytes[alignment_offset .. alignment_offset + new_length]);
}
/// Returns the largest sub-slice within the given slice that conforms to the new alignment,
/// or `null` if the given slice contains no conforming address.
pub fn alignInSlice(slice: anytype, comptime new_alignment: usize) ?AlignedSlice(@TypeOf(slice), new_alignment) {
const bytes = sliceAsBytes(slice);
const aligned_bytes = alignInBytes(bytes, new_alignment) orelse return null;
const Element = @TypeOf(slice[0]);
const slice_length_bytes = aligned_bytes.len - (aligned_bytes.len % @sizeOf(Element));
const aligned_slice = bytesAsSlice(Element, aligned_bytes[0..slice_length_bytes]);
return @alignCast(new_alignment, aligned_slice);
}

51
lib/std/os/windows.zig
View File

@@ -957,29 +957,29 @@ pub fn QueryObjectName(
handle: HANDLE,
out_buffer: []u16,
) ![]u16 {
var full_buffer: [@sizeOf(OBJECT_NAME_INFORMATION) + PATH_MAX_WIDE * 2]u8 align(@alignOf(OBJECT_NAME_INFORMATION)) = undefined;
var info = @ptrCast(*OBJECT_NAME_INFORMATION, &full_buffer);
const out_buffer_aligned = mem.alignInSlice(out_buffer, @alignOf(OBJECT_NAME_INFORMATION)) orelse return error.NameTooLong;
const info = @ptrCast(*OBJECT_NAME_INFORMATION, out_buffer_aligned);
//buffer size is specified in bytes
const out_buffer_len = std.math.cast(ULONG, out_buffer_aligned.len * 2) catch |e| switch (e) {
error.Overflow => std.math.maxInt(ULONG),
};
//last argument would return the length required for full_buffer, not exposed here
const rc = ntdll.NtQueryObject(handle, .ObjectNameInformation, &full_buffer, full_buffer.len, null);
const rc = ntdll.NtQueryObject(handle, .ObjectNameInformation, info, out_buffer_len, null);
switch (rc) {
.SUCCESS => {
// info.Name.Buffer from ObQueryNameString is documented to be null (and MaximumLength == 0)
// if the object was "unnamed", not sure if this can happen for file handles
if (info.Name.MaximumLength == 0) return error.Unexpected;
//resulting string length is specified in bytes
// resulting string length is specified in bytes
const path_length_unterminated = @divExact(info.Name.Length, 2);
if (out_buffer.len < path_length_unterminated) {
return error.NameTooLong;
}
mem.copy(WCHAR, out_buffer[0..path_length_unterminated], info.Name.Buffer[0..path_length_unterminated]);
return out_buffer[0..path_length_unterminated];
return info.Name.Buffer[0..path_length_unterminated];
},
.ACCESS_DENIED => return error.AccessDenied,
.INVALID_HANDLE => return error.InvalidHandle,
.BUFFER_OVERFLOW, .BUFFER_TOO_SMALL => return error.NameTooLong,
//name_buffer.len >= @sizeOf(OBJECT_NAME_INFORMATION) holds statically
.INFO_LENGTH_MISMATCH => unreachable,
// triggered when the buffer is too small for the OBJECT_NAME_INFORMATION object (.INFO_LENGTH_MISMATCH),
// or if the buffer is too small for the file path returned (.BUFFER_OVERFLOW, .BUFFER_TOO_SMALL)
.INFO_LENGTH_MISMATCH, .BUFFER_OVERFLOW, .BUFFER_TOO_SMALL => return error.NameTooLong,
else => |e| return unexpectedStatus(e),
}
}
@@ -994,10 +994,11 @@ test "QueryObjectName" {
var out_buffer: [PATH_MAX_WIDE]u16 = undefined;
var result_path = try QueryObjectName(handle, &out_buffer);
const required_len_in_u16 = result_path.len + @divExact(@ptrToInt(result_path.ptr) - @ptrToInt(&out_buffer), 2) + 1;
//insufficient size
std.testing.expectError(error.NameTooLong, QueryObjectName(handle, out_buffer[0 .. result_path.len - 1]));
std.testing.expectError(error.NameTooLong, QueryObjectName(handle, out_buffer[0 .. required_len_in_u16 - 1]));
//exactly-sufficient size
_ = try QueryObjectName(handle, out_buffer[0..result_path.len]);
_ = try QueryObjectName(handle, out_buffer[0..required_len_in_u16]);
}
pub const GetFinalPathNameByHandleError = error{
@@ -1029,8 +1030,7 @@ pub fn GetFinalPathNameByHandle(
fmt: GetFinalPathNameByHandleFormat,
out_buffer: []u16,
) GetFinalPathNameByHandleError![]u16 {
var path_buffer: [math.max(@sizeOf(FILE_NAME_INFORMATION), @sizeOf(OBJECT_NAME_INFORMATION)) + PATH_MAX_WIDE * 2]u8 align(@alignOf(FILE_NAME_INFORMATION)) = undefined;
const final_path = QueryObjectName(hFile, mem.bytesAsSlice(u16, &path_buffer)) catch |err| switch (err) {
const final_path = QueryObjectName(hFile, out_buffer) catch |err| switch (err) {
// we assume InvalidHandle is close enough to FileNotFound in semantics
// to not further complicate the error set
error.InvalidHandle => return error.FileNotFound,
@@ -1040,11 +1040,7 @@ pub fn GetFinalPathNameByHandle(
switch (fmt.volume_name) {
.Nt => {
// the returned path is already in .Nt format
if (out_buffer.len < final_path.len) {
return error.NameTooLong;
}
mem.copy(u16, out_buffer, final_path);
return out_buffer[0..final_path.len];
return final_path;
},
.Dos => {
// parse the string to separate volume path from file path
@@ -1153,16 +1149,17 @@ test "GetFinalPathNameByHandle" {
var buffer: [PATH_MAX_WIDE]u16 = undefined;
//check with sufficient size
const nt_length = (try GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, &buffer)).len;
const dos_length = (try GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, &buffer)).len;
const nt_path = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, &buffer);
_ = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, &buffer);
const required_len_in_u16 = nt_path.len + @divExact(@ptrToInt(nt_path.ptr) - @ptrToInt(&buffer), 2) + 1;
//check with insufficient size
std.testing.expectError(error.NameTooLong, GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, buffer[0 .. nt_length - 1]));
std.testing.expectError(error.NameTooLong, GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, buffer[0 .. dos_length - 1]));
std.testing.expectError(error.NameTooLong, GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, buffer[0 .. required_len_in_u16 - 1]));
std.testing.expectError(error.NameTooLong, GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, buffer[0 .. required_len_in_u16 - 1]));
//check with exactly-sufficient size
_ = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, buffer[0..nt_length]);
_ = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, buffer[0..dos_length]);
_ = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Nt }, buffer[0..required_len_in_u16]);
_ = try GetFinalPathNameByHandle(handle, .{ .volume_name = .Dos }, buffer[0..required_len_in_u16]);
}
pub const QueryInformationFileError = error{Unexpected};