path: root/guix/build/syscalls.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2015 David Thompson <davet@gnu.org>
;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix build syscalls)
  #:use-module (system foreign)
  #:use-module (rnrs bytevectors)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 regex)
  #:use-module (ice-9 match)
  #:use-module (ice-9 ftw)
  #:export (errno
            MS_RDONLY
            MS_NOSUID
            MS_NODEV
            MS_NOEXEC
            MS_REMOUNT
            MS_BIND
            MS_MOVE
            MS_STRICTATIME
            MNT_FORCE
            MNT_DETACH
            MNT_EXPIRE
            UMOUNT_NOFOLLOW
            restart-on-EINTR
            mount
            umount
            mount-points
            swapon
            swapoff

            file-system?
            file-system-type
            file-system-block-size
            file-system-block-count
            file-system-blocks-free
            file-system-blocks-available
            file-system-file-count
            file-system-free-file-nodes
            file-system-identifier
            file-system-maximum-name-length
            file-system-fragment-size
            file-system-mount-flags
            statfs

            processes
            mkdtemp!
            pivot-root

            CLONE_CHILD_CLEARTID
            CLONE_CHILD_SETTID
            CLONE_NEWNS
            CLONE_NEWUTS
            CLONE_NEWIPC
            CLONE_NEWUSER
            CLONE_NEWPID
            CLONE_NEWNET
            clone
            setns

            PF_PACKET
            AF_PACKET
            IFF_UP
            IFF_BROADCAST
            IFF_LOOPBACK
            all-network-interface-names
            network-interface-names
            network-interface-flags
            loopback-network-interface?
            network-interface-address
            set-network-interface-flags
            set-network-interface-address
            set-network-interface-up
            configure-network-interface

            interface?
            interface-name
            interface-flags
            interface-address
            interface-netmask
            interface-broadcast-address
            network-interfaces

            window-size?
            window-size-rows
            window-size-columns
            window-size-x-pixels
            window-size-y-pixels
            terminal-window-size
            terminal-columns))

;;; Commentary:
;;;
;;; This module provides bindings to libc's syscall wrappers.  It uses the
;;; FFI, and thus requires a dynamically-linked Guile.  (For statically-linked
;;; Guile, we instead apply 'guile-linux-syscalls.patch'.)
;;;
;;; Code:


;;;
;;; Packed structures.
;;;

(define-syntax sizeof*
  ;; XXX: This duplicates 'compile-time-value'.
  (syntax-rules (int128)
    ((_ int128)
     16)
    ((_ type)
     (let-syntax ((v (lambda (s)
                       (let ((val (sizeof type)))
                         (syntax-case s ()
                           (_ val))))))
       v))))

(define-syntax alignof*
  ;; XXX: This duplicates 'compile-time-value'.
  (syntax-rules (int128)
    ((_ int128)
     16)
    ((_ type)
     (let-syntax ((v (lambda (s)
                       (let ((val (alignof type)))
                         (syntax-case s ()
                           (_ val))))))
       v))))

(define-syntax align                             ;as found in (system foreign)
  (syntax-rules (~)
    "Add to OFFSET whatever it takes to get proper alignment for TYPE."
    ((_ offset (type ~ endianness))
     (align offset type))
    ((_ offset type)
     (1+ (logior (1- offset) (1- (alignof* type)))))))

(define-syntax type-size
  (syntax-rules (~)
    ((_ (type ~ order))
     (sizeof* type))
    ((_ type)
     (sizeof* type))))

(define-syntax struct-alignment
  (syntax-rules ()
    "Compute the alignment for the aggregate made of TYPES at OFFSET.  The
result is the alignment of the \"most strictly aligned component\"."
    ((_ offset types ...)
     (max (align offset types) ...))))

(define-syntax struct-size
  (syntax-rules ()
    "Return the size in bytes of the structure made of TYPES."
    ((_ offset (types-processed ...))
     ;; The SysV ABI P.S. says: "Aggregates (structures and arrays) and unions
     ;; assume the alignment of their most strictly aligned component."  As an
     ;; example, a struct such as "int32, int16" has size 8, not 6.
     (1+ (logior (1- offset)
                 (1- (struct-alignment offset types-processed ...)))))
    ((_ offset (types-processed ...) type0 types ...)
     (struct-size (+ (type-size type0) (align offset type0))
                  (type0 types-processed ...)
                  types ...))))

(define-syntax write-type
  (syntax-rules (~)
    ((_ bv offset (type ~ order) value)
     (bytevector-uint-set! bv offset value
                           (endianness order) (sizeof* type)))
    ((_ bv offset type value)
     (bytevector-uint-set! bv offset value
                           (native-endianness) (sizeof* type)))))

(define-syntax write-types
  (syntax-rules ()
    ((_ bv offset () ())
     #t)
    ((_ bv offset (type0 types ...) (field0 fields ...))
     (begin
       (write-type bv (align offset type0) type0 field0)
       (write-types bv
                    (+ (align offset type0) (type-size type0))
                    (types ...) (fields ...))))))

(define-syntax read-type
  (syntax-rules (~ quote *)
    ((_ bv offset '*)
     (make-pointer (bytevector-uint-ref bv offset
                                        (native-endianness)
                                        (sizeof* '*))))
    ((_ bv offset (type ~ order))
     (bytevector-uint-ref bv offset
                          (endianness order) (sizeof* type)))
    ((_ bv offset type)
     (bytevector-uint-ref bv offset
                          (native-endianness) (sizeof* type)))))

(define-syntax read-types
  (syntax-rules ()
    ((_ return bv offset () (values ...))
     (return values ...))
    ((_ return bv offset (type0 types ...) (values ...))
     (read-types return
                 bv
                 (+ (align offset type0) (type-size type0))
                 (types ...)
                 (values ... (read-type bv
                                        (align offset type0)
                                        type0))))))

(define-syntax define-c-struct
  (syntax-rules ()
    "Define SIZE as the size in bytes of the C structure made of FIELDS.  READ
as a deserializer and WRITE! as a serializer for the C structure with the
given TYPES.  READ uses WRAP-FIELDS to return its value."
    ((_ name size wrap-fields read write! (fields types) ...)
     (begin
       (define size
         (struct-size 0 () types ...))
       (define (write! bv offset fields ...)
         (write-types bv offset (types ...) (fields ...)))
       (define* (read bv #:optional (offset 0))
         (read-types wrap-fields bv offset (types ...) ()))))))


;;;
;;; FFI.
;;;

(define %libc-errno-pointer
  ;; Glibc's 'errno' pointer.
  (let ((errno-loc (dynamic-func "__errno_location" (dynamic-link))))
    (and errno-loc
         (let ((proc (pointer->procedure '* errno-loc '())))
           (proc)))))

(define errno
  (if %libc-errno-pointer
      (let ((bv (pointer->bytevector %libc-errno-pointer (sizeof int))))
        (lambda ()
          "Return the current errno."
          ;; XXX: We assume that nothing changes 'errno' while we're doing all this.
          ;; In particular, that means that no async must be running here.

          ;; Use one of the fixed-size native-ref procedures because they are
          ;; optimized down to a single VM instruction, which reduces the risk
          ;; that we fiddle with 'errno' (needed on Guile 2.0.5, libc 2.11.)
          (let-syntax ((ref (lambda (s)
                              (syntax-case s ()
                                ((_ bv)
                                 (case (sizeof int)
                                   ((4)
                                    #'(bytevector-s32-native-ref bv 0))
                                   ((8)
                                    #'(bytevector-s64-native-ref bv 0))
                                   (else
                                    (error "unsupported 'int' size"
                                           (sizeof int)))))))))
            (ref bv))))
      (lambda () 0)))

(define (call-with-restart-on-EINTR thunk)
  (let loop ()
    (catch 'system-error
      thunk
      (lambda args
        (if (= (system-error-errno args) EINTR)
            (loop)
            (apply throw args))))))

(define-syntax-rule (restart-on-EINTR expr)
  "Evaluate EXPR and restart upon EINTR.  Return the value of EXPR."
  (call-with-restart-on-EINTR (lambda () expr)))

(define (syscall->procedure return-type name argument-types)
  "Return a procedure that wraps the C function NAME using the dynamic FFI.
If an error occurs while creating the binding, defer the error report until
the returned procedure is called."
  (catch #t
    (lambda ()
      (let ((ptr (dynamic-func name (dynamic-link))))
        (pointer->procedure return-type ptr argument-types)))
    (lambda args
      (lambda _
        (error (format #f "~a: syscall->procedure failed: ~s"
                       name args))))))


;;;
;;; File systems.
;;;

(define (augment-mtab source target type options)
  "Augment /etc/mtab with information about the given mount point."
  (let ((port (open-file "/etc/mtab" "a")))
    (format port "~a ~a ~a ~a 0 0~%"
            source target type (or options "rw"))
    (close-port port)))

(define (read-mtab port)
  "Read an mtab-formatted file from PORT, returning a list of tuples."
  (let loop ((result '()))
    (let ((line (read-line port)))
      (if (eof-object? line)
          (reverse result)
          (loop (cons (string-tokenize line) result))))))

(define (remove-from-mtab target)
  "Remove mount point TARGET from /etc/mtab."
  (define entries
    (remove (match-lambda
             ((device mount-point type options freq passno)
              (string=? target mount-point))
             (_ #f))
            (call-with-input-file "/etc/mtab" read-mtab)))

  (call-with-output-file "/etc/mtab"
    (lambda (port)
      (for-each (match-lambda
                 ((device mount-point type options freq passno)
                  (format port "~a ~a ~a ~a ~a ~a~%"
                          device mount-point type options freq passno)))
                entries))))

;; Linux mount flags, from libc's <sys/mount.h>.
(define MS_RDONLY             1)
(define MS_NOSUID             2)
(define MS_NODEV              4)
(define MS_NOEXEC             8)
(define MS_REMOUNT           32)
(define MS_BIND            4096)
(define MS_MOVE            8192)
(define MS_STRICTATIME 16777216)

(define MNT_FORCE       1)
(define MNT_DETACH      2)
(define MNT_EXPIRE      4)
(define UMOUNT_NOFOLLOW 8)

(define mount
  (let ((proc (syscall->procedure int "mount" `(* * * ,unsigned-long *))))
    (lambda* (source target type #:optional (flags 0) options
                     #:key (update-mtab? #f))
      "Mount device SOURCE on TARGET as a file system TYPE.  Optionally, FLAGS
may be a bitwise-or of the MS_* <sys/mount.h> constants, and OPTIONS may be a
string.  When FLAGS contains MS_REMOUNT, SOURCE and TYPE are ignored.  When
UPDATE-MTAB? is true, update /etc/mtab.  Raise a 'system-error' exception on
error."
      (let ((ret (proc (if source
                           (string->pointer source)
                           %null-pointer)
                       (string->pointer target)
                       (if type
                           (string->pointer type)
                           %null-pointer)
                       flags
                       (if options
                           (string->pointer options)
                           %null-pointer)))
            (err (errno)))
        (unless (zero? ret)
          (throw 'system-error "mount" "mount ~S on ~S: ~A"
                 (list source target (strerror err))
                 (list err)))
        (when update-mtab?
          (augment-mtab source target type options))))))

(define umount
  (let ((proc (syscall->procedure int "umount2" `(* ,int))))
    (lambda* (target #:optional (flags 0)
                     #:key (update-mtab? #f))
      "Unmount TARGET.  Optionally FLAGS may be one of the MNT_* or UMOUNT_*
constants from <sys/mount.h>."
      (let ((ret (proc (string->pointer target) flags))
            (err (errno)))
        (unless (zero? ret)
          (throw 'system-error "umount" "~S: ~A"
                 (list target (strerror err))
                 (list err)))
        (when update-mtab?
          (remove-from-mtab target))))))

(define (mount-points)
  "Return the mounts points for currently mounted file systems."
  (call-with-input-file "/proc/mounts"
    (lambda (port)
      (let loop ((result '()))
        (let ((line (read-line port)))
          (if (eof-object? line)
              (reverse result)
              (match (string-tokenize line)
                ((source mount-point _ ...)
                 (loop (cons mount-point result))))))))))

(define swapon
  (let ((proc (syscall->procedure int "swapon" (list '* int))))
    (lambda* (device #:optional (flags 0))
      "Use the block special device at DEVICE for swapping."
      (let ((ret (proc (string->pointer device) flags))
            (err (errno)))
        (unless (zero? ret)
          (throw 'system-error "swapon" "~S: ~A"
                 (list device (strerror err))
                 (list err)))))))

(define swapoff
  (let ((proc (syscall->procedure int "swapoff" '(*))))
    (lambda (device)
      "Stop using block special device DEVICE for swapping."
      (let ((ret (proc (string->pointer device)))
            (err (errno)))
        (unless (zero? ret)
          (throw 'system-error "swapoff" "~S: ~A"
                 (list device (strerror err))
                 (list err)))))))

(define (kernel? pid)
  "Return #t if PID designates a \"kernel thread\" rather than a normal
user-land process."
  (let ((stat (call-with-input-file (format #f "/proc/~a/stat" pid)
                (compose string-tokenize read-string))))
    ;; See proc.txt in Linux's documentation for the list of fields.
    (match stat
      ((pid tcomm state ppid pgrp sid tty_nr tty_pgrp flags min_flt
            cmin_flt maj_flt cmaj_flt utime stime cutime cstime
            priority nice num_thread it_real_value start_time
            vsize rss rsslim
            (= string->number start_code) (= string->number end_code) _ ...)
       ;; Got this obscure trick from sysvinit's 'killall5' program.
       (and (zero? start_code) (zero? end_code))))))

(define (processes)
  "Return the list of live processes."
  (sort (filter-map (lambda (file)
                      (let ((pid (string->number file)))
                        (and pid
                             (not (kernel? pid))
                             pid)))
                    (scandir "/proc"))
        <))

(define mkdtemp!
  (let* ((ptr  (dynamic-func "mkdtemp" (dynamic-link)))
         (proc (pointer->procedure '* ptr '(*))))
    (lambda (tmpl)
      "Create a new unique directory in the file system using the template
string TMPL and return its file name.  TMPL must end with 'XXXXXX'."
      (let ((result (proc (string->pointer tmpl)))
            (err    (errno)))
        (when (null-pointer? result)
          (throw 'system-error "mkdtemp!" "~S: ~A"
                 (list tmpl (strerror err))
                 (list err)))
        (pointer->string result)))))


(define-record-type <file-system>
  (file-system type block-size blocks blocks-free
               blocks-available files free-files identifier
               name-length fragment-size mount-flags spare0 spare1)
  file-system?
  (type              file-system-type)
  (block-size        file-system-block-size)
  (blocks            file-system-block-count)
  (blocks-free       file-system-blocks-free)
  (blocks-available  file-system-blocks-available)
  (files             file-system-file-count)
  (free-files        file-system-free-file-nodes)
  (identifier        file-system-identifier)
  (name-length       file-system-maximum-name-length)
  (fragment-size     file-system-fragment-size)
  (mount-flags       file-system-mount-flags)
  (spare0            file-system--spare0)
  (spare1            file-system--spare1))

(define-syntax fsword                             ;fsword_t
  (identifier-syntax long))

(define-c-struct %statfs                          ;<bits/statfs.h>
  sizeof-statfs                                   ;slightly overestimated
  file-system
  read-statfs
  write-statfs!
  (type             fsword)
  (block-size       fsword)
  (blocks           uint64)
  (blocks-free      uint64)
  (blocks-available uint64)
  (files            uint64)
  (free-files       uint64)
  (identifier       uint64)                       ;really "int[2]"
  (name-length      fsword)
  (fragment-size    fsword)
  (mount-flags      fsword)
  (spare0           int128)                       ;really "fsword[4]"
  (spare1           int128))

(define statfs
  (let ((proc (syscall->procedure int "statfs" '(* *))))
    (lambda (file)
      "Return a <file-system> data structure describing the file system
mounted at FILE."
      (let* ((stat (make-bytevector sizeof-statfs))
             (ret  (proc (string->pointer file) (bytevector->pointer stat)))
             (err  (errno)))
        (if (zero? ret)
            (read-statfs stat 0)
            (throw 'system-error "statfs" "~A: ~A"
                   (list file (strerror err))
                   (list err)))))))


;;;
;;; Containers.
;;;

;; Linux clone flags, from linux/sched.h
(define CLONE_CHILD_CLEARTID #x00200000)
(define CLONE_CHILD_SETTID   #x01000000)
(define CLONE_NEWNS          #x00020000)
(define CLONE_NEWUTS         #x04000000)
(define CLONE_NEWIPC         #x08000000)
(define CLONE_NEWUSER        #x10000000)
(define CLONE_NEWPID         #x20000000)
(define CLONE_NEWNET         #x40000000)

;; The libc interface to sys_clone is not useful for Scheme programs, so the
;; low-level system call is wrapped instead.  The 'syscall' function is
;; declared in <unistd.h> as a variadic function; in practice, it expects 6
;; pointer-sized arguments, as shown in, e.g., x86_64/syscall.S.
(define clone
  (let* ((proc (syscall->procedure int "syscall"
                                   (list long                   ;sysno
                                         unsigned-long          ;flags
                                         '* '* '*
                                         '*)))
         ;; TODO: Don't do this.
         (syscall-id (match (utsname:machine (uname))
                       ("i686"   120)
                       ("x86_64" 56)
                       ("mips64" 5055)
                       ("armv7l" 120)
                       (_ #f))))
    (lambda (flags)
      "Create a new child process by duplicating the current parent process.
Unlike the fork system call, clone accepts FLAGS that specify which resources
are shared between the parent and child processes."
      (let ((ret (proc syscall-id flags
                       %null-pointer               ;child stack
                       %null-pointer %null-pointer ;ptid & ctid
                       %null-pointer))             ;unused
            (err (errno)))
        (if (= ret -1)
            (throw 'system-error "clone" "~d: ~A"
                   (list flags (strerror err))
                   (list err))
            ret)))))

(define setns
  ;; Some systems may be using an old (pre-2.14) version of glibc where there
  ;; is no 'setns' function available.
  (false-if-exception
   (let* ((ptr  (dynamic-func "setns" (dynamic-link)))
          (proc (pointer->procedure int ptr (list int int))))
     (lambda (fdes nstype)
       "Reassociate the current process with the namespace specified by FDES, a
file descriptor obtained by opening a /proc/PID/ns/* file.  NSTYPE specifies
which type of namespace the current process may be reassociated with, or 0 if
there is no such limitation."
       (let ((ret (proc fdes nstype))
             (err (errno)))
         (unless (zero? ret)
           (throw 'system-error "setns" "~d ~d: ~A"
                  (list fdes nstype (strerror err))
                  (list err))))))))

(define pivot-root
  (let ((proc (syscall->procedure int "pivot_root" (list '* '*))))
    (lambda (new-root put-old)
      "Change the root file system to NEW-ROOT and move the current root file
system to PUT-OLD."
      (let ((ret (proc (string->pointer new-root)
                       (string->pointer put-old)))
            (err (errno)))
        (unless (zero? ret)
          (throw 'system-error "pivot_root" "~S ~S: ~A"
                 (list new-root put-old (strerror err))
                 (list err)))))))


;;;
;;; Network interfaces.
;;;

(define SIOCGIFCONF                               ;from <bits/ioctls.h>
  (if (string-contains %host-type "linux")
      #x8912                                      ;GNU/Linux
      #xf00801a4))                                ;GNU/Hurd
(define SIOCGIFFLAGS
  (if (string-contains %host-type "linux")
      #x8913                                      ;GNU/Linux
      #xc4804191))                                ;GNU/Hurd
(define SIOCSIFFLAGS
  (if (string-contains %host-type "linux")
      #x8914                                      ;GNU/Linux
      -1))                                        ;FIXME: GNU/Hurd?
(define SIOCGIFADDR
  (if (string-contains %host-type "linux")
      #x8915                                      ;GNU/Linux
      -1))                                        ;FIXME: GNU/Hurd?
(define SIOCSIFADDR
  (if (string-contains %host-type "linux")
      #x8916                                      ;GNU/Linux
      -1))                                        ;FIXME: GNU/Hurd?

;; Flags and constants from <net/if.h>.

(define IFF_UP #x1)                               ;Interface is up
(define IFF_BROADCAST #x2)                        ;Broadcast address valid.
(define IFF_LOOPBACK #x8)                         ;Is a loopback net.

(define IF_NAMESIZE 16)                           ;maximum interface name size

(define ifconf-struct
  ;; 'struct ifconf', from <net/if.h>.
  (list int                                       ;int ifc_len
        '*))                                      ;struct ifreq *ifc_ifcu

(define ifreq-struct-size
  ;; 'struct ifreq' begins with an array of IF_NAMESIZE bytes containing the
  ;; interface name (nul-terminated), followed by a bunch of stuff.  This is
  ;; its size in bytes.
  (if (= 8 (sizeof '*))
      40
      32))

(define-c-struct sockaddr-in                      ;<linux/in.h>
  sizeof-sockaddrin
  (lambda (family port address)
    (make-socket-address family address port))
  read-sockaddr-in
  write-sockaddr-in!
  (family    unsigned-short)
  (port      (int16 ~ big))
  (address   (int32 ~ big)))

(define-c-struct sockaddr-in6                     ;<linux/in6.h>
  sizeof-sockaddr-in6
  (lambda (family port flowinfo address scopeid)
    (make-socket-address family address port flowinfo scopeid))
  read-sockaddr-in6
  write-sockaddr-in6!
  (family    unsigned-short)
  (port      (int16 ~ big))
  (flowinfo  (int32 ~ big))
  (address   (int128 ~ big))
  (scopeid   int32))

(define (write-socket-address! sockaddr bv index)
  "Write SOCKADDR, a socket address as returned by 'make-socket-address', to
bytevector BV at INDEX."
  (let ((family (sockaddr:fam sockaddr)))
    (cond ((= family AF_INET)
           (write-sockaddr-in! bv index
                               family
                               (sockaddr:port sockaddr)
                               (sockaddr:addr sockaddr)))
          ((= family AF_INET6)
           (write-sockaddr-in6! bv index
                                family
                                (sockaddr:port sockaddr)
                                (sockaddr:flowinfo sockaddr)
                                (sockaddr:addr sockaddr)
                                (sockaddr:scopeid sockaddr)))
          (else
           (error "unsupported socket address" sockaddr)))))

(define PF_PACKET 17)                             ;<bits/socket.h>
(define AF_PACKET PF_PACKET)

(define* (read-socket-address bv #:optional (index 0))
  "Read a socket address from bytevector BV at INDEX."
  (let ((family (bytevector-u16-native-ref bv index)))
    (cond ((= family AF_INET)
           (read-sockaddr-in bv index))
          ((= family AF_INET6)
           (read-sockaddr-in6 bv index))
          (else
           ;; XXX: Unsupported address family, such as AF_PACKET.  Return a
           ;; vector such that the vector can at least call 'sockaddr:fam'.
           (vector family)))))

(define %ioctl
  ;; The most terrible interface, live from Scheme.
  (pointer->procedure int
                      (dynamic-func "ioctl" (dynamic-link))
                      (list int unsigned-long '*)))

(define (bytevector->string-list bv stride len)
  "Return the null-terminated strings found in BV every STRIDE bytes.  Read at
most LEN bytes from BV."
  (let loop ((bytes  (take (bytevector->u8-list bv)
                           (min len (bytevector-length bv))))
             (result '()))
    (match bytes
      (()
       (reverse result))
      (_
       (loop (drop bytes stride)
             (cons (list->string (map integer->char
                                      (take-while (negate zero?) bytes)))
                   result))))))

(define* (network-interface-names #:optional sock)
  "Return the names of existing network interfaces.  This is typically limited
to interfaces that are currently up."
  (let* ((close? (not sock))
         (sock   (or sock (socket SOCK_STREAM AF_INET 0)))
         (len    (* ifreq-struct-size 10))
         (reqs   (make-bytevector len))
         (conf   (make-c-struct ifconf-struct
                                (list len (bytevector->pointer reqs))))
         (ret    (%ioctl (fileno sock) SIOCGIFCONF conf))
         (err    (errno)))
    (when close?
      (close-port sock))
    (if (zero? ret)
        (bytevector->string-list reqs ifreq-struct-size
                                 (match (parse-c-struct conf ifconf-struct)
                                   ((len . _) len)))
        (throw 'system-error "network-interface-list"
               "network-interface-list: ~A"
               (list (strerror err))
               (list err)))))

(define %interface-line
  ;; Regexp matching an interface line in Linux's /proc/net/dev.
  (make-regexp "^[[:blank:]]*([[:graph:]]+):.*$"))

(define (all-network-interface-names)
  "Return all the names of the registered network interfaces, including those
that are not up."
  (call-with-input-file "/proc/net/dev"           ;XXX: Linux-specific
    (lambda (port)
      (let loop ((interfaces '()))
        (let ((line (read-line port)))
          (cond ((eof-object? line)
                 (reverse interfaces))
                ((regexp-exec %interface-line line)
                 =>
                 (lambda (match)
                   (loop (cons (match:substring match 1) interfaces))))
                (else
                 (loop interfaces))))))))

(define (network-interface-flags socket name)
  "Return a number that is the bit-wise or of 'IFF*' flags for network
interface NAME."
  (let ((req (make-bytevector ifreq-struct-size)))
    (bytevector-copy! (string->utf8 name) 0 req 0
                      (min (string-length name) (- IF_NAMESIZE 1)))
    (let* ((ret (%ioctl (fileno socket) SIOCGIFFLAGS
                        (bytevector->pointer req)))
           (err (errno)))
      (if (zero? ret)

          ;; The 'ifr_flags' field is IF_NAMESIZE bytes after the beginning of
          ;; 'struct ifreq', and it's a short int.
          (bytevector-sint-ref req IF_NAMESIZE (native-endianness)
                               (sizeof short))

          (throw 'system-error "network-interface-flags"
                 "network-interface-flags on ~A: ~A"
                 (list name (strerror err))
                 (list err))))))

(define (loopback-network-interface? name)
  "Return true if NAME designates a loopback network interface."
  (let* ((sock  (socket SOCK_STREAM AF_INET 0))
         (flags (network-interface-flags sock name)))
    (close-port sock)
    (not (zero? (logand flags IFF_LOOPBACK)))))

(define (set-network-interface-flags socket name flags)
  "Set the flag of network interface NAME to FLAGS."
  (let ((req (make-bytevector ifreq-struct-size)))
    (bytevector-copy! (string->utf8 name) 0 req 0
                      (min (string-length name) (- IF_NAMESIZE 1)))
    ;; Set the 'ifr_flags' field.
    (bytevector-uint-set! req IF_NAMESIZE flags (native-endianness)
                          (sizeof short))
    (let* ((ret (%ioctl (fileno socket) SIOCSIFFLAGS
                        (bytevector->pointer req)))
           (err (errno)))
      (unless (zero? ret)
        (throw 'system-error "set-network-interface-flags"
               "set-network-interface-flags on ~A: ~A"
               (list name (strerror err))
               (list err))))))

(define (set-network-interface-address socket name sockaddr)
  "Set the address of network interface NAME to SOCKADDR."
  (let ((req (make-bytevector ifreq-struct-size)))
    (bytevector-copy! (string->utf8 name) 0 req 0
                      (min (string-length name) (- IF_NAMESIZE 1)))
    ;; Set the 'ifr_addr' field.
    (write-socket-address! sockaddr req IF_NAMESIZE)
    (let* ((ret (%ioctl (fileno socket) SIOCSIFADDR
                        (bytevector->pointer req)))
           (err (errno)))
      (unless (zero? ret)
        (throw 'system-error "set-network-interface-address"
               "set-network-interface-address on ~A: ~A"
               (list name (strerror err))
               (list err))))))

(define (network-interface-address socket name)
  "Return the address of network interface NAME.  The result is an object of
the same type as that returned by 'make-socket-address'."
  (let ((req (make-bytevector ifreq-struct-size)))
    (bytevector-copy! (string->utf8 name) 0 req 0
                      (min (string-length name) (- IF_NAMESIZE 1)))
    (let* ((ret (%ioctl (fileno socket) SIOCGIFADDR
                        (bytevector->pointer req)))
           (err (errno)))
      (if (zero? ret)
          (read-socket-address req IF_NAMESIZE)
          (throw 'system-error "network-interface-address"
                 "network-interface-address on ~A: ~A"
                 (list name (strerror err))
                 (list err))))))

(define (configure-network-interface name sockaddr flags)
  "Configure network interface NAME to use SOCKADDR, an address as returned by
'make-socket-address', and FLAGS, a bitwise-or of IFF_* constants."
  (let ((sock (socket (sockaddr:fam sockaddr) SOCK_STREAM 0)))
    (dynamic-wind
      (const #t)
      (lambda ()
        (set-network-interface-address sock name sockaddr)
        (set-network-interface-flags sock name flags))
      (lambda ()
        (close-port sock)))))

(define* (set-network-interface-up name
                                   #:key (family AF_INET))
  "Turn up the interface NAME."
  (let ((sock (socket family SOCK_STREAM 0)))
    (dynamic-wind
      (const #t)
      (lambda ()
        (let ((flags (network-interface-flags sock name)))
          (set-network-interface-flags sock name
                                       (logior flags IFF_UP))))
      (lambda ()
        (close-port sock)))))


;;;
;;; Details about network interfaces---aka. 'getifaddrs'.
;;;

;; Network interfaces.  XXX: We would call it <network-interface> but that
;; would collide with the ioctl wrappers above.
(define-record-type <interface>
  (make-interface name flags address netmask broadcast-address)
  interface?
  (name              interface-name)               ;string
  (flags             interface-flags)              ;or'd IFF_* values
  (address           interface-address)            ;sockaddr | #f
  (netmask           interface-netmask)            ;sockaddr | #f
  (broadcast-address interface-broadcast-address)) ;sockaddr | #f

(define (write-interface interface port)
  (match interface
    (($ <interface> name flags address)
     (format port "#<interface ~s " name)
     (unless (zero? (logand IFF_UP flags))
       (display "up " port))

     ;; Check whether ADDRESS really is a sockaddr.
     (when address
       (if (member (sockaddr:fam address) (list AF_INET AF_INET6))
           (format port "~a " (inet-ntop (sockaddr:fam address)
                                         (sockaddr:addr address)))
           (format port "family:~a " (sockaddr:fam address))))

     (format port "~a>" (number->string (object-address interface) 16)))))

(set-record-type-printer! <interface> write-interface)

(define (values->interface next name flags address netmask
                           broadcast-address data)
  "Given the raw field values passed as arguments, return a pair whose car is
an <interface> object, and whose cdr is the pointer NEXT."
  (define (maybe-socket-address pointer)
    (if (null-pointer? pointer)
        #f
        (read-socket-address (pointer->bytevector pointer 50)))) ;XXX: size

  (cons (make-interface (if (null-pointer? name)
                            #f
                            (pointer->string name))
                        flags
                        (maybe-socket-address address)
                        (maybe-socket-address netmask)
                        (maybe-socket-address broadcast-address)
                        ;; Ignore DATA.
                        )
        next))

(define-c-struct ifaddrs                          ;<ifaddrs.h>
  %sizeof-ifaddrs
  values->interface
  read-ifaddrs
  write-ifaddrs!
  (next          '*)
  (name          '*)
  (flags         unsigned-int)
  (addr          '*)
  (netmask       '*)
  (broadcastaddr '*)
  (data          '*))

(define (unfold-interface-list ptr)
  "Call 'read-ifaddrs' on PTR and all its 'next' fields, recursively, and
return the list of resulting <interface> objects."
  (let loop ((ptr    ptr)
             (result '()))
    (if (null-pointer? ptr)
        (reverse result)
        (match (read-ifaddrs (pointer->bytevector ptr %sizeof-ifaddrs))
          ((ifaddr . ptr)
           (loop ptr (cons ifaddr result)))))))

(define network-interfaces
  (let* ((ptr  (dynamic-func "getifaddrs" (dynamic-link)))
         (proc (pointer->procedure int ptr (list '*))))
    (lambda ()
      "Return a list of <interface> objects, each denoting a configured
network interface.  This is implemented using the 'getifaddrs' libc function."
      (let* ((ptr (bytevector->pointer (make-bytevector (sizeof* '*))))
             (ret (proc ptr))
             (err (errno)))
        (if (zero? ret)
            (let* ((ptr    (dereference-pointer ptr))
                   (result (unfold-interface-list ptr)))
              (free-ifaddrs ptr)
              result)
            (throw 'system-error "network-interfaces" "~A"
                   (list (strerror err))
                   (list err)))))))

(define free-ifaddrs
  (let ((ptr (dynamic-func "freeifaddrs" (dynamic-link))))
    (pointer->procedure void ptr '(*))))


;;;
;;; Terminals.
;;;

(define-syntax TIOCGWINSZ                         ;<asm-generic/ioctls.h>
  (identifier-syntax #x5413))

(define-record-type <window-size>
  (window-size rows columns x-pixels y-pixels)
  window-size?
  (rows     window-size-rows)
  (columns  window-size-columns)
  (x-pixels window-size-x-pixels)
  (y-pixels window-size-y-pixels))

(define-c-struct winsize                          ;<bits/ioctl-types.h>
  sizeof-winsize
  window-size
  read-winsize
  write-winsize!
  (rows          unsigned-short)
  (columns       unsigned-short)
  (x-pixels      unsigned-short)
  (y-pixels      unsigned-short))

(define* (terminal-window-size #:optional (port (current-output-port)))
  "Return a <window-size> structure describing the terminal at PORT, or raise
a 'system-error' if PORT is not backed by a terminal.  This procedure
corresponds to the TIOCGWINSZ ioctl."
  (let* ((size (make-bytevector sizeof-winsize))
         (ret  (%ioctl (fileno port) TIOCGWINSZ
                       (bytevector->pointer size)))
         (err  (errno)))
    (if (zero? ret)
        (read-winsize size)
        (throw 'system-error "terminal-window-size" "~A"
               (list (strerror err))
               (list err)))))

(define* (terminal-columns #:optional (port (current-output-port)))
  "Return the best approximation of the number of columns of the terminal at
PORT, trying to guess a reasonable value if all else fails.  The result is
always a positive integer."
  (define (fall-back)
    (match (and=> (getenv "COLUMNS") string->number)
      (#f 80)
      ((? number? columns)
       (if (> columns 0) columns 80))))

  (catch 'system-error
    (lambda ()
      (if (file-port? port)
          (match (window-size-columns (terminal-window-size port))
            ;; Things like Emacs shell-mode return 0, which is unreasonable.
            (0 (fall-back))
            ((? number? columns) columns))
          (fall-back)))
    (lambda args
      (let ((errno (system-error-errno args)))
        ;; ENOTTY is what we're after but 2012-and-earlier Linux versions
        ;; would return EINVAL instead in some cases:
        ;; <https://bugs.ruby-lang.org/issues/10494>.
        (if (or (= errno ENOTTY) (= errno EINVAL))
            (fall-back)
            (apply throw args))))))

;;; syscalls.scm ends here