[PATCH 2/3] define function to print error messages to user log

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at librato.com):
> 
> 
> Serge E. Hallyn wrote:
> > Error messages are both sent to an optional user-provided logfile,
> > and, if CONFIG_CHECKPOINT_DEBUG=y, sent to syslog.
> > 
> > Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
> > ---
> >  checkpoint/objhash.c             |    2 +
> >  checkpoint/sys.c                 |   61 ++++++++++++++++++++++++++++++++++---
> >  include/linux/checkpoint.h       |    2 +-
> >  include/linux/checkpoint_types.h |    1 +
> >  include/linux/syscalls.h         |    5 ++-
> >  5 files changed, 63 insertions(+), 8 deletions(-)
> > 
> > diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
> > index 730dd82..c441ce6 100644
> > --- a/checkpoint/objhash.c
> > +++ b/checkpoint/objhash.c
> > @@ -858,6 +858,8 @@ int ckpt_obj_contained(struct ckpt_ctx *ctx)
> >  
> >  	/* account for ctx->file reference (if in the table already) */
> >  	ckpt_obj_users_inc(ctx, ctx->file, 1);
> > +	if (ctx->logfile)
> > +		ckpt_obj_users_inc(ctx, ctx->logfile, 1);
> >  	/* account for ctx->root_nsproxy reference (if in the table already) */
> >  	ckpt_obj_users_inc(ctx, ctx->root_nsproxy, 1);
> >  
> > diff --git a/checkpoint/sys.c b/checkpoint/sys.c
> > index 260a1ee..1840f90 100644
> > --- a/checkpoint/sys.c
> > +++ b/checkpoint/sys.c
> > @@ -204,6 +204,8 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
> >  
> >  	if (ctx->file)
> >  		fput(ctx->file);
> > +	if (ctx->logfile)
> > +		fput(ctx->logfile);
> >  
> >  	ckpt_obj_hash_free(ctx);
> >  	path_put(&ctx->fs_mnt);
> > @@ -225,7 +227,7 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
> >  }
> >  
> >  static struct ckpt_ctx *ckpt_ctx_alloc(int fd, unsigned long uflags,
> > -				       unsigned long kflags)
> > +				       unsigned long kflags, int logfd)
> >  {
> >  	struct ckpt_ctx *ctx;
> >  	int err;
> > @@ -238,6 +240,9 @@ static struct ckpt_ctx *ckpt_ctx_alloc(int fd, unsigned long uflags,
> >  	ctx->kflags = kflags;
> >  	ctx->ktime_begin = ktime_get();
> >  
> > +	/* If logfd's a bad fd that's fine, no log output required... */
> > +	ctx->logfile = fget(logfd);
> 
> Can we make it more user-friendly, e.g. f logfd==-1 then no logfile,
> otherwise if fget(logfd) fails then return -EBADF ?
> 
> > +
> >  	atomic_set(&ctx->refcount, 0);
> >  	INIT_LIST_HEAD(&ctx->pgarr_list);
> >  	INIT_LIST_HEAD(&ctx->pgarr_pool);
> > @@ -339,6 +344,51 @@ int walk_task_subtree(struct task_struct *root,
> >  	return (ret < 0 ? ret : total);
> >  }
> >  
> > +/*
> > + * currentpid:targetpid fmt%args
> > + */
> > +void ckpt_log_error(struct ckpt_ctx *ctx, char *fmt, ...)
> > +{
> 
> As I commented before, I really wish not to go through this again.
> Can we come up with a mechanism for error messages, that will set
> a "standard" format (like I tried to do in ckpt_write_err) ?
> 
> (I like Matt's suggestion to use one format string instead of two,
> and allow "%(T)" constructs for our format directives).
> 
> Also, I assume some of that code can be reused here below.

Perhaps we should be using the audit system.

-serge