[CRIU] [PATCHv2 4/5] locks: Add leases c/r for kernels v4.0 and older

[Pavel Emelyanov]

On 08/14/2017 02:49 AM, Pavel Begunkov wrote:
> Information about locks in /proc/<pid>/fdinfo is presented only since
> kernel v4.1. This patch adds logic to *note_file_lock* to match leases
> and OFDs.

OFDs? Can you shed more light on this, why have OFDs popped up?

> Signed-off-by: Pavel Begunkov <asml.silence at gmail.com>
> ---
>  criu/file-lock.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 83 insertions(+), 2 deletions(-)
> 
> diff --git a/criu/file-lock.c b/criu/file-lock.c
> index 5b0580782..b7462dc77 100644
> --- a/criu/file-lock.c
> +++ b/criu/file-lock.c
> @@ -266,6 +266,81 @@ static int lock_ofd_check_fd(int lfd, struct file_lock *fl)
>  	return 1;
>  }
>  
> +static int lease_check_fd(int fd, int file_flags, struct file_lock *fl)
> +{
> +	int file_lease_type, err;
> +	int lease_type = fl->fl_ltype & (~LEASE_BREAKING);
> +
> +	if ((file_flags & O_ACCMODE) != O_RDONLY) {
> +		/*
> +		 * Write OFD conflicts with any lease not associated
> +		 * with it, therefore there is can't be other lease
> +		 * or OFD for this file.
> +		 */
> +		return 1;
> +	}
> +
> +	file_lease_type = fcntl(fd, F_GETLEASE);
> +	if (file_lease_type < 0) {
> +		pr_err("Can't get lease type\n");
> +		return -1;
> +	}
> +
> +	/*
> +	 * Only read OFDs can be present for the file. If
> +	 * read and write OFDs with at least one lease had
> +	 * presented, it would have conflicted.
> +	 */
> +	if (fl->fl_ltype & LEASE_BREAKING) {
> +		/*
> +		 * Only read leases are possible for read OFDs
> +		 * and they all should be in breaking state,
> +		 * because the current one is.
> +		 */
> +		int compatible_type = file_lease_type;
> +
> +		if (compatible_type != F_UNLCK) {
> +			pr_err("Lease doesn't conflicts but breaks\n");
> +			return -1;
> +		}
> +
> +		/*
> +		 * Due to activated breaking sequence we can't
> +		 * get actual lease type with F_GETLEASE.
> +		 * The err == 0 after lease upgrade means, that
> +		 * there is already read lease. Otherwise it
> +		 * will fail because of breaking sequence.
> +		 */
> +		err = fcntl(fd, F_SETLEASE, F_RDLCK);
> +		if (err < 0) {
> +			if (errno != EAGAIN) {
> +				pr_perror("Can't set lease (fd %i)", fd);
> +				return -1;
> +			}
> +			return 0;
> +		} else {
> +			return 1;
> +		}
> +	} else {
> +		/*
> +		 * The file can have only non-breaking read
> +		 * leases, because otherwise the current one
> +		 * also would have broke.
> +		 */
> +		if (lease_type != F_RDLCK) {
> +			pr_err("Incorrect lease type\n");
> +			return -1;
> +		}
> +
> +		if (file_lease_type == F_UNLCK)
> +			return 0;
> +		if (file_lease_type == F_RDLCK)
> +			return 1;
> +		pr_err("Invalid file lease type\n");
> +		return -1;
> +	}
> +}
> +
>  int note_file_lock(struct pid *pid, int fd, int lfd, struct fd_parms *p)
>  {
>  	struct file_lock *fl;
> @@ -295,8 +370,14 @@ int note_file_lock(struct pid *pid, int fd, int lfd, struct fd_parms *p)
>  			if (fl->fl_owner != pid->real)
>  				continue;
>  		} else if (fl->fl_kind == FL_LEASE) {
> -			pr_err("Leases are not supported for kernel <= v4.0");
> -			return -1;
> +			if (fl->owners_fd >= 0)
> +				continue;
> +
> +			ret = lease_check_fd(lfd, p->flags, fl);
> +			if (ret < 0)
> +				return ret;
> +			if (ret == 0)
> +				continue;
>  		} else /* fl->fl_kind == FL_FLOCK || fl->fl_kind == FL_OFD */ {
>  			int ret;
>  
>