diff options
Diffstat (limited to 'guix/build/syscalls.scm')
| -rw-r--r-- | guix/build/syscalls.scm | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm index a9cd6e93c8..86723c23c7 100644 --- a/guix/build/syscalls.scm +++ b/guix/build/syscalls.scm @@ -65,6 +65,7 @@ processes mkdtemp! pivot-root + fcntl-flock CLONE_CHILD_CLEARTID CLONE_CHILD_SETTID @@ -639,6 +640,74 @@ system to PUT-OLD." ;;; +;;; Advisory file locking. +;;; + +(define %struct-flock + ;; 'struct flock' from <fcntl.h>. + (list short ; l_type + short ; l_whence + size_t ; l_start + size_t ; l_len + int)) ; l_pid + +(define F_SETLKW + ;; On Linux-based systems, this is usually 7, but not always + ;; (exceptions include SPARC.) On GNU/Hurd, it's 9. + (cond ((string-contains %host-type "sparc") 9) ; sparc-*-linux-gnu + ((string-contains %host-type "linux") 7) ; *-linux-gnu + (else 9))) ; *-gnu* + +(define F_SETLK + ;; Likewise: GNU/Hurd and SPARC use 8, while the others typically use 6. + (cond ((string-contains %host-type "sparc") 8) ; sparc-*-linux-gnu + ((string-contains %host-type "linux") 6) ; *-linux-gnu + (else 8))) ; *-gnu* + +(define F_xxLCK + ;; The F_RDLCK, F_WRLCK, and F_UNLCK constants. + (cond ((string-contains %host-type "sparc") #(1 2 3)) ; sparc-*-linux-gnu + ((string-contains %host-type "hppa") #(1 2 3)) ; hppa-*-linux-gnu + ((string-contains %host-type "linux") #(0 1 2)) ; *-linux-gnu + (else #(1 2 3)))) ; *-gnu* + +(define fcntl-flock + (let ((proc (syscall->procedure int "fcntl" `(,int ,int *)))) + (lambda* (fd-or-port operation #:key (wait? #t)) + "Perform locking OPERATION on the file beneath FD-OR-PORT. OPERATION +must be a symbol, one of 'read-lock, 'write-lock, or 'unlock. When WAIT? is +true, block until the lock is acquired; otherwise, thrown an 'flock-error' +exception if it's already taken." + (define (operation->int op) + (case op + ((read-lock) (vector-ref F_xxLCK 0)) + ((write-lock) (vector-ref F_xxLCK 1)) + ((unlock) (vector-ref F_xxLCK 2)) + (else (error "invalid fcntl-flock operation" op)))) + + (define fd + (if (port? fd-or-port) + (fileno fd-or-port) + fd-or-port)) + + ;; XXX: 'fcntl' is a vararg function, but here we happily use the + ;; standard ABI; crossing fingers. + (let ((err (proc fd + (if wait? + F_SETLKW ; lock & wait + F_SETLK) ; non-blocking attempt + (make-c-struct %struct-flock + (list (operation->int operation) + SEEK_SET + 0 0 ; whole file + 0))))) + (or (zero? err) + + ;; Presumably we got EAGAIN or so. + (throw 'flock-error (errno))))))) + + +;;; ;;; Network interfaces. ;;; |