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  • Davide Libenzi's avatar
    signal/timer/event: signalfd core · fba2afaa
    Davide Libenzi authored
    This patch series implements the new signalfd() system call.
    
    I took part of the original Linus code (and you know how badly it can be
    broken :), and I added even more breakage ;) Signals are fetched from the same
    signal queue used by the process, so signalfd will compete with standard
    kernel delivery in dequeue_signal().  If you want to reliably fetch signals on
    the signalfd file, you need to block them with sigprocmask(SIG_BLOCK).  This
    seems to be working fine on my Dual Opteron machine.  I made a quick test
    program for it:
    
    http://www.xmailserver.org/signafd-test.c
    
    
    
    The signalfd() system call implements signal delivery into a file descriptor
    receiver.  The signalfd file descriptor if created with the following API:
    
    int signalfd(int ufd, const sigset_t *mask, size_t masksize);
    
    The "ufd" parameter allows to change an existing signalfd sigmask, w/out going
    to close/create cycle (Linus idea).  Use "ufd" == -1 if you want a brand new
    signalfd file.
    
    The "mask" allows to specify the signal mask of signals that we are interested
    in.  The "masksize" parameter is the size of "mask".
    
    The signalfd fd supports the poll(2) and read(2) system calls.  The poll(2)
    will return POLLIN when signals are available to be dequeued.  As a direct
    consequence of supporting the Linux poll subsystem, the signalfd fd can use
    used together with epoll(2) too.
    
    The read(2) system call will return a "struct signalfd_siginfo" structure in
    the userspace supplied buffer.  The return value is the number of bytes copied
    in the supplied buffer, or -1 in case of error.  The read(2) call can also
    return 0, in case the sighand structure to which the signalfd was attached,
    has been orphaned.  The O_NONBLOCK flag is also supported, and read(2) will
    return -EAGAIN in case no signal is available.
    
    If the size of the buffer passed to read(2) is lower than sizeof(struct
    signalfd_siginfo), -EINVAL is returned.  A read from the signalfd can also
    return -ERESTARTSYS in case a signal hits the process.  The format of the
    struct signalfd_siginfo is, and the valid fields depends of the (->code &
    __SI_MASK) value, in the same way a struct siginfo would:
    
    struct signalfd_siginfo {
    	__u32 signo;	/* si_signo */
    	__s32 err;	/* si_errno */
    	__s32 code;	/* si_code */
    	__u32 pid;	/* si_pid */
    	__u32 uid;	/* si_uid */
    	__s32 fd;	/* si_fd */
    	__u32 tid;	/* si_fd */
    	__u32 band;	/* si_band */
    	__u32 overrun;	/* si_overrun */
    	__u32 trapno;	/* si_trapno */
    	__s32 status;	/* si_status */
    	__s32 svint;	/* si_int */
    	__u64 svptr;	/* si_ptr */
    	__u64 utime;	/* si_utime */
    	__u64 stime;	/* si_stime */
    	__u64 addr;	/* si_addr */
    };
    
    [akpm@linux-foundation.org: fix signalfd_copyinfo() on i386]
    Signed-off-by: default avatarDavide Libenzi <davidel@xmailserver.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fba2afaa