Merge branch 'lun-4-linux-memfd-create'

Closes #3687

6 files changed, 111 insertions, 0 deletions

diff --git a/lib/std/c/linux.zig b/lib/std/c/linux.zig
index 5b45b49332..9969474097 100644
--- a/lib/std/c/linux.zig
+++ b/lib/std/c/linux.zig
@@ -76,6 +76,8 @@ pub extern "c" fn dl_iterate_phdr(callback: dl_iterate_phdr_callback, data: ?*c_
 
 pub extern "c" fn sigaltstack(ss: ?*stack_t, old_ss: ?*stack_t) c_int;
 
+pub extern "c" fn memfd_create(name: [*:0]const u8, flags: c_uint) c_int;
+
 pub const pthread_attr_t = extern struct {
     __size: [56]u8,
     __align: c_long,
diff --git a/lib/std/os.zig b/lib/std/os.zig
index f7426faeda..878d1a57e7 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -3281,3 +3281,47 @@ pub fn setsockopt(fd: fd_t, level: u32, optname: u32, opt: []const u8) SetSockOp
         else => |err| return unexpectedErrno(err),
     }
 }
+
+pub const MemFdCreateError = error{
+    SystemFdQuotaExceeded,
+    ProcessFdQuotaExceeded,
+    OutOfMemory,
+
+    /// memfd_create is available in Linux 3.17 and later. This error is returned
+    /// for older kernel versions.
+    SystemOutdated,
+} || UnexpectedError;
+
+pub fn memfd_createC(name: [*:0]const u8, flags: u32) MemFdCreateError!fd_t {
+    // memfd_create is available only in glibc versions starting with 2.27.
+    const use_c = std.c.versionCheck(.{ .major = 2, .minor = 27, .patch = 0 }).ok;
+    const sys = if (use_c) std.c else linux;
+    const getErrno = if (use_c) std.c.getErrno else linux.getErrno;
+    const rc = sys.memfd_create(name, flags);
+    switch (getErrno(rc)) {
+        0 => return @intCast(fd_t, rc),
+        EFAULT => unreachable, // name has invalid memory
+        EINVAL => unreachable, // name/flags are faulty
+        ENFILE => return error.SystemFdQuotaExceeded,
+        EMFILE => return error.ProcessFdQuotaExceeded,
+        ENOMEM => return error.OutOfMemory,
+        ENOSYS => return error.SystemOutdated,
+        else => |err| return unexpectedErrno(err),
+    }
+}
+
+pub const MFD_NAME_PREFIX = "memfd:";
+pub const MFD_MAX_NAME_LEN = NAME_MAX - MFD_NAME_PREFIX.len;
+fn toMemFdPath(name: []const u8) ![MFD_MAX_NAME_LEN:0]u8 {
+    var path_with_null: [MFD_MAX_NAME_LEN:0]u8 = undefined;
+    // >= rather than > to make room for the null byte
+    if (name.len >= MFD_MAX_NAME_LEN) return error.NameTooLong;
+    mem.copy(u8, &path_with_null, name);
+    path_with_null[name.len] = 0;
+    return path_with_null;
+}
+
+pub fn memfd_create(name: []const u8, flags: u32) !fd_t {
+    const name_t = try toMemFdPath(name);
+    return memfd_createC(&name_t, flags);
+}
diff --git a/lib/std/os/bits/linux.zig b/lib/std/os/bits/linux.zig
index 8033f27c2b..3fb160e3ec 100644
--- a/lib/std/os/bits/linux.zig
+++ b/lib/std/os/bits/linux.zig
@@ -26,6 +26,7 @@ pub const uid_t = i32;
 pub const gid_t = u32;
 pub const clock_t = isize;
 
+pub const NAME_MAX = 255;
 pub const PATH_MAX = 4096;
 pub const IOV_MAX = 1024;
 
@@ -1417,3 +1418,38 @@ pub const POLLHUP = 0x010;
 pub const POLLNVAL = 0x020;
 pub const POLLRDNORM = 0x040;
 pub const POLLRDBAND = 0x080;
+
+pub const MFD_CLOEXEC = 0x0001;
+pub const MFD_ALLOW_SEALING = 0x0002;
+pub const MFD_HUGETLB = 0x0004;
+pub const MFD_ALL_FLAGS = MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB;
+
+pub const HUGETLB_FLAG_ENCODE_SHIFT = 26;
+pub const HUGETLB_FLAG_ENCODE_MASK = 0x3f;
+pub const HUGETLB_FLAG_ENCODE_64KB = 16 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_512KB = 19 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_1MB = 20 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_2MB = 21 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_8MB = 23 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_16MB = 24 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_32MB = 25 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_256MB = 28 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_512MB = 29 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_1GB = 30 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_2GB = 31 << HUGETLB_FLAG_ENCODE_SHIFT;
+pub const HUGETLB_FLAG_ENCODE_16GB = 34 << HUGETLB_FLAG_ENCODE_SHIFT;
+
+pub const MFD_HUGE_SHIFT = HUGETLB_FLAG_ENCODE_SHIFT;
+pub const MFD_HUGE_MASK = HUGETLB_FLAG_ENCODE_MASK;
+pub const MFD_HUGE_64KB = HUGETLB_FLAG_ENCODE_64KB;
+pub const MFD_HUGE_512KB = HUGETLB_FLAG_ENCODE_512KB;
+pub const MFD_HUGE_1MB = HUGETLB_FLAG_ENCODE_1MB;
+pub const MFD_HUGE_2MB = HUGETLB_FLAG_ENCODE_2MB;
+pub const MFD_HUGE_8MB = HUGETLB_FLAG_ENCODE_8MB;
+pub const MFD_HUGE_16MB = HUGETLB_FLAG_ENCODE_16MB;
+pub const MFD_HUGE_32MB = HUGETLB_FLAG_ENCODE_32MB;
+pub const MFD_HUGE_256MB = HUGETLB_FLAG_ENCODE_256MB;
+pub const MFD_HUGE_512MB = HUGETLB_FLAG_ENCODE_512MB;
+pub const MFD_HUGE_1GB = HUGETLB_FLAG_ENCODE_1GB;
+pub const MFD_HUGE_2GB = HUGETLB_FLAG_ENCODE_2GB;
+pub const MFD_HUGE_16GB = HUGETLB_FLAG_ENCODE_16GB;
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index d5bab64493..b6030fe2fe 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -1110,6 +1110,10 @@ pub fn io_uring_register(fd: i32, opcode: u32, arg: ?*const c_void, nr_args: u32
     return syscall4(SYS_io_uring_register, @bitCast(usize, @as(isize, fd)), opcode, @ptrToInt(arg), nr_args);
 }
 
+pub fn memfd_create(name: [*:0]const u8, flags: u32) usize {
+    return syscall2(SYS_memfd_create, @ptrToInt(name), flags);
+}
+
 test "" {
     if (builtin.os == .linux) {
         _ = @import("linux/test.zig");
diff --git a/lib/std/os/test.zig b/lib/std/os/test.zig
index f61e8b4657..09e8c24899 100644
--- a/lib/std/os/test.zig
+++ b/lib/std/os/test.zig
@@ -237,3 +237,21 @@ test "argsAlloc" {
     var args = try std.process.argsAlloc(std.heap.page_allocator);
     std.process.argsFree(std.heap.page_allocator, args);
 }
+
+test "memfd_create" {
+    // memfd_create is linux specific.
+    if (builtin.os != .linux) return error.SkipZigTest;
+    const fd = std.os.memfd_create("test", 0) catch |err| switch (err) {
+        // Related: https://github.com/ziglang/zig/issues/4019
+        error.SystemOutdated => return error.SkipZigTest,
+        else => |e| return e,
+    };
+    defer std.os.close(fd);
+    try std.os.write(fd, "test");
+    try std.os.lseek_SET(fd, 0);
+
+    var buf: [10]u8 = undefined;
+    const bytes_read = try std.os.read(fd, &buf);
+    expect(bytes_read == 4);
+    expect(mem.eql(u8, buf[0..4], "test"));
+}
diff --git a/lib/std/target.zig b/lib/std/target.zig
index 50c749d30b..22fea691c4 100644
--- a/lib/std/target.zig
+++ b/lib/std/target.zig
@@ -597,6 +597,13 @@ pub const Target = union(enum) {
         };
     }
 
+    pub fn isMusl(self: Target) bool {
+        return switch (self.getAbi()) {
+            .musl, .musleabi, .musleabihf => true,
+            else => false,
+        };
+    }
+
     pub fn isDarwin(self: Target) bool {
         return switch (self.getOs()) {
             .ios, .macosx, .watchos, .tvos => true,