[PATCH] xfs_db: redirect printfs when metadumping to stdout

[PATCH] xfs_db: redirect printfs when metadumping to stdout

[Darrick J. Wong]

If we're metadumping to stdout, we don't want xfs_db's various dbprintf
statements dumping to stdout because that'll corrupt the metadump.
Therefore, let outf point to the existing stdout and redirect stdout to
stderr for the duration of the dump operation.

Reported-by: David Shaw <dshaw@jabberwocky.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 db/metadump.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/db/metadump.c b/db/metadump.c
index e046f60..e6e153d 100644
--- a/db/metadump.c
+++ b/db/metadump.c
@@ -2874,6 +2874,7 @@ metadump_f(
 	xfs_agnumber_t	agno;
 	int		c;
 	int		start_iocur_sp;
+	bool		stdout_metadump = false;
 	char		*p;
 
 	exitcode = 1;
@@ -2989,6 +2990,8 @@ metadump_f(
 			return 0;
 		}
 		outf = stdout;
+		stdout = stderr;
+		stdout_metadump = true;
 	} else {
 		outf = fopen(argv[optind], "wb");
 		if (outf == NULL) {
@@ -3020,9 +3023,11 @@ metadump_f(
 		exitcode = write_index() < 0;
 
 	if (progress_since_warning)
-		fputc('\n', (outf == stdout) ? stderr : stdout);
+		fputc('\n', stdout_metadump ? stderr : stdout);
 
-	if (outf != stdout)
+	if (stdout_metadump)
+		stdout = outf;
+	else
 		fclose(outf);
 
 	/* cleanup iocur stack */

Re: [PATCH] xfs_db: redirect printfs when metadumping to stdout

[Eric Sandeen]

On 07/14/2017 06:30 PM, Darrick J. Wong wrote:
> If we're metadumping to stdout, we don't want xfs_db's various dbprintf
> statements dumping to stdout because that'll corrupt the metadump.
> Therefore, let outf point to the existing stdout and redirect stdout to
> stderr for the duration of the dump operation.
> 
> Reported-by: David Shaw <dshaw@jabberwocky.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  db/metadump.c |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/db/metadump.c b/db/metadump.c
> index e046f60..e6e153d 100644
> --- a/db/metadump.c
> +++ b/db/metadump.c
> @@ -2874,6 +2874,7 @@ metadump_f(
>  	xfs_agnumber_t	agno;
>  	int		c;
>  	int		start_iocur_sp;
> +	bool		stdout_metadump = false;
>  	char		*p;
>  
>  	exitcode = 1;
> @@ -2989,6 +2990,8 @@ metadump_f(
>  			return 0;
>  		}
>  		outf = stdout;
> +		stdout = stderr;
> +		stdout_metadump = true;

Ok, I ... guess?  xfs_metadump already takes pains to
print to stderr as appropriate; see print_warning(), and comments
about where "wornings" should go.

But in this case I guess it's the guts of db / dbprintf that caused the
problems, right?  ... yup you said that in the commit message.

I suppose a comment:

/* Move stdout to stderr so thta xfs_db warnings don't pollute metadump stream */

or something would help the future reader know why you had to do this.

it feels a little hacky but I don't really see a particularly better way I guess.

-Eric

>  	} else {
>  		outf = fopen(argv[optind], "wb");
>  		if (outf == NULL) {
> @@ -3020,9 +3023,11 @@ metadump_f(
>  		exitcode = write_index() < 0;
>  
>  	if (progress_since_warning)
> -		fputc('\n', (outf == stdout) ? stderr : stdout);
> +		fputc('\n', stdout_metadump ? stderr : stdout);
>  
> -	if (outf != stdout)
> +	if (stdout_metadump)
> +		stdout = outf;
> +	else
>  		fclose(outf);
>  
>  	/* cleanup iocur stack */
>