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    Subject[PATCH 091/109] kernel: add ksys_setsid() helper; remove in-kernel call to sys_setsid()
    Date
    Using this helper allows us to avoid the in-kernel call to the
    sys_setsid() syscall. The ksys_ prefix denotes that this function
    is meant as a drop-in replacement for the syscall. In particular, it
    uses the same calling convention as sys_setsid().

    This patch is part of a series which removes in-kernel calls to syscalls.
    On this basis, the syscall entry path can be streamlined. For details, see
    http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    ---
    include/linux/syscalls.h | 1 +
    init/do_mounts_initrd.c | 2 +-
    kernel/sys.c | 7 ++++++-
    3 files changed, 8 insertions(+), 2 deletions(-)

    diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
    index e724dda509e0..4dd685ee425d 100644
    --- a/include/linux/syscalls.h
    +++ b/include/linux/syscalls.h
    @@ -962,6 +962,7 @@ off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence);
    ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count);
    void ksys_sync(void);
    int ksys_unshare(unsigned long unshare_flags);
    +int ksys_setsid(void);

    /*
    * The following kernel syscall equivalents are just wrappers to fs-internal
    diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
    index d1d3e53bdeef..5a91aefa7305 100644
    --- a/init/do_mounts_initrd.c
    +++ b/init/do_mounts_initrd.c
    @@ -45,7 +45,7 @@ static int init_linuxrc(struct subprocess_info *info, struct cred *new)
    ksys_chdir("/root");
    ksys_mount(".", "/", NULL, MS_MOVE, NULL);
    ksys_chroot(".");
    - sys_setsid();
    + ksys_setsid();
    return 0;
    }

    diff --git a/kernel/sys.c b/kernel/sys.c
    index 550f47788ae4..ad692183dfe9 100644
    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -1150,7 +1150,7 @@ static void set_special_pids(struct pid *pid)
    change_pid(curr, PIDTYPE_PGID, pid);
    }

    -SYSCALL_DEFINE0(setsid)
    +int ksys_setsid(void)
    {
    struct task_struct *group_leader = current->group_leader;
    struct pid *sid = task_pid(group_leader);
    @@ -1183,6 +1183,11 @@ SYSCALL_DEFINE0(setsid)
    return err;
    }

    +SYSCALL_DEFINE0(setsid)
    +{
    + return ksys_setsid();
    +}
    +
    DECLARE_RWSEM(uts_sem);

    #ifdef COMPAT_UTS_MACHINE
    --
    2.16.3
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