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std.Build.Watch: key fanotify file descriptors by mount id
Since marks are limited to a single filesystem. Context: ziglang#20670 Original pull request: ziglang#20672 Co-authored-by: Maciej 'vesim' Kuliński <vesim809@pm.me>
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‎lib/std/Build/Watch.zig

Lines changed: 56 additions & 47 deletions
Original file line numberDiff line numberDiff line change
@@ -33,9 +33,12 @@ const Os = switch (builtin.os.tag) {
3333

3434
/// Keyed differently but indexes correspond 1:1 with `dir_table`.
3535
handle_table: HandleTable,
36-
poll_fds: [1]posix.pollfd,
36+
/// fanotify file descriptors are keyed by mount id since marks
37+
/// are limited to a single filesystem.
38+
poll_fds: std.AutoArrayHashMapUnmanaged(MountId, posix.pollfd),
3739

38-
const HandleTable = std.ArrayHashMapUnmanaged(FileHandle, ReactionSet, FileHandle.Adapter, false);
40+
const MountId = i32;
41+
const HandleTable = std.ArrayHashMapUnmanaged(FileHandle, struct { mount_id: MountId, reaction_set: ReactionSet }, FileHandle.Adapter, false);
3942

4043
const fan_mask: std.os.linux.fanotify.MarkMask = .{
4144
.CLOSE_WRITE = true,
@@ -92,53 +95,33 @@ const Os = switch (builtin.os.tag) {
9295
};
9396

9497
fn init() !Watch {
95-
const fan_fd = std.posix.fanotify_init(.{
96-
.CLASS = .NOTIF,
97-
.CLOEXEC = true,
98-
.NONBLOCK = true,
99-
.REPORT_NAME = true,
100-
.REPORT_DIR_FID = true,
101-
.REPORT_FID = true,
102-
.REPORT_TARGET_FID = true,
103-
}, 0) catch |err| switch (err) {
104-
error.UnsupportedFlags => fatal("fanotify_init failed due to old kernel; requires 5.17+", .{}),
105-
else => |e| return e,
106-
};
10798
return .{
10899
.dir_table = .{},
109100
.os = switch (builtin.os.tag) {
110101
.linux => .{
111102
.handle_table = .{},
112-
.poll_fds = .{
113-
.{
114-
.fd = fan_fd,
115-
.events = std.posix.POLL.IN,
116-
.revents = undefined,
117-
},
118-
},
103+
.poll_fds = .{},
119104
},
120105
else => {},
121106
},
122107
.generation = 0,
123108
};
124109
}
125110

126-
fn getDirHandle(gpa: Allocator, path: std.Build.Cache.Path) !FileHandle {
111+
fn getDirHandle(gpa: Allocator, path: std.Build.Cache.Path, mount_id: *MountId) !FileHandle {
127112
var file_handle_buffer: [@sizeOf(std.os.linux.file_handle) + 128]u8 align(@alignOf(std.os.linux.file_handle)) = undefined;
128-
var mount_id: i32 = undefined;
129113
var buf: [std.fs.max_path_bytes]u8 = undefined;
130114
const adjusted_path = if (path.sub_path.len == 0) "./" else std.fmt.bufPrint(&buf, "{s}/", .{
131115
path.sub_path,
132116
}) catch return error.NameTooLong;
133117
const stack_ptr: *std.os.linux.file_handle = @ptrCast(&file_handle_buffer);
134118
stack_ptr.handle_bytes = file_handle_buffer.len - @sizeOf(std.os.linux.file_handle);
135-
try posix.name_to_handle_at(path.root_dir.handle.fd, adjusted_path, stack_ptr, &mount_id, std.os.linux.AT.HANDLE_FID);
119+
try posix.name_to_handle_at(path.root_dir.handle.fd, adjusted_path, stack_ptr, mount_id, std.os.linux.AT.HANDLE_FID);
136120
const stack_lfh: FileHandle = .{ .handle = stack_ptr };
137121
return stack_lfh.clone(gpa);
138122
}
139123

140-
fn markDirtySteps(w: *Watch, gpa: Allocator) !bool {
141-
const fan_fd = w.os.getFanFd();
124+
fn markDirtySteps(w: *Watch, gpa: Allocator, fan_fd: posix.fd_t) !bool {
142125
const fanotify = std.os.linux.fanotify;
143126
const M = fanotify.event_metadata;
144127
var events_buf: [256 + 4096]u8 = undefined;
@@ -167,10 +150,10 @@ const Os = switch (builtin.os.tag) {
167150
const file_name_z: [*:0]u8 = @ptrCast((&file_handle.f_handle).ptr + file_handle.handle_bytes);
168151
const file_name = std.mem.span(file_name_z);
169152
const lfh: FileHandle = .{ .handle = file_handle };
170-
if (w.os.handle_table.getPtr(lfh)) |reaction_set| {
171-
if (reaction_set.getPtr(".")) |glob_set|
153+
if (w.os.handle_table.getPtr(lfh)) |value| {
154+
if (value.reaction_set.getPtr(".")) |glob_set|
172155
any_dirty = markStepSetDirty(gpa, glob_set, any_dirty);
173-
if (reaction_set.getPtr(file_name)) |step_set|
156+
if (value.reaction_set.getPtr(file_name)) |step_set|
174157
any_dirty = markStepSetDirty(gpa, step_set, any_dirty);
175158
}
176159
},
@@ -180,19 +163,38 @@ const Os = switch (builtin.os.tag) {
180163
}
181164
}
182165

183-
fn getFanFd(os: *const @This()) posix.fd_t {
184-
return os.poll_fds[0].fd;
185-
}
186-
187166
fn update(w: *Watch, gpa: Allocator, steps: []const *Step) !void {
188-
const fan_fd = w.os.getFanFd();
189167
// Add missing marks and note persisted ones.
190168
for (steps) |step| {
191169
for (step.inputs.table.keys(), step.inputs.table.values()) |path, *files| {
192170
const reaction_set = rs: {
193171
const gop = try w.dir_table.getOrPut(gpa, path);
194172
if (!gop.found_existing) {
195-
const dir_handle = try Os.getDirHandle(gpa, path);
173+
var mount_id: MountId = undefined;
174+
const dir_handle = try Os.getDirHandle(gpa, path, &mount_id);
175+
const fan_fd = blk: {
176+
const fd_gop = try w.os.poll_fds.getOrPut(gpa, mount_id);
177+
if (!fd_gop.found_existing) {
178+
const fan_fd = std.posix.fanotify_init(.{
179+
.CLASS = .NOTIF,
180+
.CLOEXEC = true,
181+
.NONBLOCK = true,
182+
.REPORT_NAME = true,
183+
.REPORT_DIR_FID = true,
184+
.REPORT_FID = true,
185+
.REPORT_TARGET_FID = true,
186+
}, 0) catch |err| switch (err) {
187+
error.UnsupportedFlags => fatal("fanotify_init failed due to old kernel; requires 5.17+", .{}),
188+
else => |e| return e,
189+
};
190+
fd_gop.value_ptr.* = .{
191+
.fd = fan_fd,
192+
.events = std.posix.POLL.IN,
193+
.revents = undefined,
194+
};
195+
}
196+
break :blk fd_gop.value_ptr.*.fd;
197+
};
196198
// `dir_handle` may already be present in the table in
197199
// the case that we have multiple Cache.Path instances
198200
// that compare inequal but ultimately point to the same
@@ -204,17 +206,17 @@ const Os = switch (builtin.os.tag) {
204206
_ = w.dir_table.pop();
205207
} else {
206208
assert(dh_gop.index == gop.index);
207-
dh_gop.value_ptr.* = .{};
209+
dh_gop.value_ptr.* = .{ .mount_id = mount_id, .reaction_set = .{} };
208210
posix.fanotify_mark(fan_fd, .{
209211
.ADD = true,
210212
.ONLYDIR = true,
211213
}, fan_mask, path.root_dir.handle.fd, path.subPathOrDot()) catch |err| {
212214
fatal("unable to watch {}: {s}", .{ path, @errorName(err) });
213215
};
214216
}
215-
break :rs dh_gop.value_ptr;
217+
break :rs &dh_gop.value_ptr.reaction_set;
216218
}
217-
break :rs &w.os.handle_table.values()[gop.index];
219+
break :rs &w.os.handle_table.values()[gop.index].reaction_set;
218220
};
219221
for (files.items) |basename| {
220222
const gop = try reaction_set.getOrPut(gpa, basename);
@@ -229,7 +231,7 @@ const Os = switch (builtin.os.tag) {
229231
var i: usize = 0;
230232
while (i < w.os.handle_table.entries.len) {
231233
{
232-
const reaction_set = &w.os.handle_table.values()[i];
234+
const reaction_set = &w.os.handle_table.values()[i].reaction_set;
233235
var step_set_i: usize = 0;
234236
while (step_set_i < reaction_set.entries.len) {
235237
const step_set = &reaction_set.values()[step_set_i];
@@ -256,6 +258,8 @@ const Os = switch (builtin.os.tag) {
256258

257259
const path = w.dir_table.keys()[i];
258260

261+
const mount_id = w.os.handle_table.values()[i].mount_id;
262+
const fan_fd = w.os.poll_fds.getEntry(mount_id).?.value_ptr.fd;
259263
posix.fanotify_mark(fan_fd, .{
260264
.REMOVE = true,
261265
.ONLYDIR = true,
@@ -272,13 +276,14 @@ const Os = switch (builtin.os.tag) {
272276
}
273277

274278
fn wait(w: *Watch, gpa: Allocator, timeout: Timeout) !WaitResult {
275-
const events_len = try std.posix.poll(&w.os.poll_fds, timeout.to_i32_ms());
276-
return if (events_len == 0)
277-
.timeout
278-
else if (try Os.markDirtySteps(w, gpa))
279-
.dirty
280-
else
281-
.clean;
279+
const events_len = try std.posix.poll(w.os.poll_fds.values(), timeout.to_i32_ms());
280+
if (events_len == 0)
281+
return .timeout;
282+
for (w.os.poll_fds.values()) |poll_fd| {
283+
if (poll_fd.revents & std.posix.POLL.IN == std.posix.POLL.IN and try Os.markDirtySteps(w, gpa, poll_fd.fd))
284+
return .dirty;
285+
}
286+
return .clean;
282287
}
283288
},
284289
.windows => struct {
@@ -838,7 +843,11 @@ pub const Match = struct {
838843
};
839844

840845
fn markAllFilesDirty(w: *Watch, gpa: Allocator) void {
841-
for (w.os.handle_table.values()) |reaction_set| {
846+
for (w.os.handle_table.values()) |value| {
847+
const reaction_set = switch (builtin.os.tag) {
848+
.linux => value.reaction_set,
849+
else => value,
850+
};
842851
for (reaction_set.values()) |step_set| {
843852
for (step_set.keys()) |step| {
844853
step.recursiveReset(gpa);

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