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Watch: Create fanotify per mount_id #20672

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Watch: Create fanotify per mount_id #20672

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88 changes: 50 additions & 38 deletions lib/std/Build/Watch.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -14,14 +14,16 @@ generation: Generation,
/// interested in noticing changes to.
///
/// Value is generation.
const DirTable = std.ArrayHashMapUnmanaged(Cache.Path, void, Cache.Path.TableAdapter, false);
const DirTable = std.ArrayHashMapUnmanaged(Cache.Path, MountId, Cache.Path.TableAdapter, false);
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I think that because this is a Linux-specific change, that this is the wrong place to add MountId and should instead be moved inside the Linux-specific Os struct defined below in this file.

For example, I use DirTable in this windows implementation where this MountId wouldn’t be needed.

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Indeed, I will make that adjustment prior to merging. Thanks.


/// Special key of "." means any changes in this directory trigger the steps.
const ReactionSet = std.StringArrayHashMapUnmanaged(StepSet);
const StepSet = std.AutoArrayHashMapUnmanaged(*Step, Generation);

const Generation = u8;

const MountId = i32;

const Hash = std.hash.Wyhash;
const Cache = std.Build.Cache;

Expand All @@ -31,7 +33,8 @@ const Os = switch (builtin.os.tag) {

/// Keyed differently but indexes correspond 1:1 with `dir_table`.
handle_table: HandleTable,
poll_fds: [1]posix.pollfd,
// mount_id -> fanotify
poll_fds: std.AutoArrayHashMapUnmanaged(MountId, posix.pollfd),

const HandleTable = std.ArrayHashMapUnmanaged(FileHandle, ReactionSet, FileHandle.Adapter, false);

Expand Down Expand Up @@ -89,22 +92,20 @@ const Os = switch (builtin.os.tag) {
};
};

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

fn markDirtySteps(w: *Watch, gpa: Allocator) !bool {
const fan_fd = w.os.getFanFd();
fn markDirtySteps(w: *Watch, gpa: Allocator, fan_fd: posix.fd_t) !bool {
const fanotify = std.os.linux.fanotify;
const M = fanotify.event_metadata;
var events_buf: [256 + 4096]u8 = undefined;
Expand Down Expand Up @@ -146,19 +147,36 @@ const Os = switch (builtin.os.tag) {
}
}

fn getFanFd(os: *const @This()) posix.fd_t {
return os.poll_fds[0].fd;
}

fn update(w: *Watch, gpa: Allocator, steps: []const *Step) !void {
const fan_fd = w.os.getFanFd();
// Add missing marks and note persisted ones.
for (steps) |step| {
for (step.inputs.table.keys(), step.inputs.table.values()) |path, *files| {
const reaction_set = rs: {
const gop = try w.dir_table.getOrPut(gpa, path);
if (!gop.found_existing) {
const dir_handle = try Os.getDirHandle(gpa, path);
var mount_id: MountId = undefined;
const dir_handle = try Os.getDirHandle(gpa, path, &mount_id);

const fan_fd = blk: {
const fd_gop = try w.os.poll_fds.getOrPut(gpa, mount_id);
if (!fd_gop.found_existing) {
const fd = try std.posix.fanotify_init(.{
.CLASS = .NOTIF,
.CLOEXEC = true,
.NONBLOCK = true,
.REPORT_NAME = true,
.REPORT_DIR_FID = true,
.REPORT_FID = true,
.REPORT_TARGET_FID = true,
}, 0);
fd_gop.value_ptr.* = .{
.fd = fd,
.events = std.posix.POLL.IN,
.revents = undefined,
};
}
break :blk fd_gop.value_ptr.*.fd;
};
// `dir_handle` may already be present in the table in
// the case that we have multiple Cache.Path instances
// that compare inequal but ultimately point to the same
Expand All @@ -175,9 +193,10 @@ const Os = switch (builtin.os.tag) {
.ADD = true,
.ONLYDIR = true,
}, fan_mask, path.root_dir.handle.fd, path.subPathOrDot()) catch |err| {
fatal("unable to watch {}: {s}", .{ path, @errorName(err) });
std.log.err("unable to watch {}: {s}", .{ path, @errorName(err) });
};
}
gop.value_ptr.* = mount_id;
break :rs dh_gop.value_ptr;
}
break :rs &w.os.handle_table.values()[gop.index];
Expand Down Expand Up @@ -221,7 +240,8 @@ const Os = switch (builtin.os.tag) {
}

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

const mount_fd = w.dir_table.values()[i];
const fan_fd = w.os.poll_fds.getEntry(mount_fd).?.value_ptr.fd;
posix.fanotify_mark(fan_fd, .{
.REMOVE = true,
.ONLYDIR = true,
Expand All @@ -243,27 +263,12 @@ const Os = switch (builtin.os.tag) {
pub fn init() !Watch {
switch (builtin.os.tag) {
.linux => {
const fan_fd = try std.posix.fanotify_init(.{
.CLASS = .NOTIF,
.CLOEXEC = true,
.NONBLOCK = true,
.REPORT_NAME = true,
.REPORT_DIR_FID = true,
.REPORT_FID = true,
.REPORT_TARGET_FID = true,
}, 0);
return .{
.dir_table = .{},
.os = switch (builtin.os.tag) {
.linux => .{
.handle_table = .{},
.poll_fds = .{
.{
.fd = fan_fd,
.events = std.posix.POLL.IN,
.revents = undefined,
},
},
.poll_fds = .{},
},
else => {},
},
Expand Down Expand Up @@ -350,13 +355,20 @@ pub const WaitResult = enum {
pub fn wait(w: *Watch, gpa: Allocator, timeout: Timeout) !WaitResult {
switch (builtin.os.tag) {
.linux => {
const events_len = try std.posix.poll(&w.os.poll_fds, timeout.to_i32_ms());
return if (events_len == 0)
.timeout
else if (try Os.markDirtySteps(w, gpa))
.dirty
else
.clean;
const events_len = try std.posix.poll(w.os.poll_fds.values(), timeout.to_i32_ms());

if (events_len == 0)
return .timeout;

for (w.os.poll_fds.values()) |poll_fd| {
var any_dirty: bool = false;
if (poll_fd.revents & std.posix.POLL.IN == std.posix.POLL.IN and
try Os.markDirtySteps(w, gpa, poll_fd.fd))
any_dirty = true;
if (any_dirty) return .dirty;
}

return .clean;
},
else => @compileError("unimplemented"),
}
Expand Down