[PATCH v2] xfs_db: redirect printfs when metadumping to stdout

[PATCH v2] 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>
---
v2: Better comments.
---
 db/metadump.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/db/metadump.c b/db/metadump.c
index e046f60..b58acef 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;
@@ -2988,7 +2989,15 @@ metadump_f(
 			free(metablock);
 			return 0;
 		}
+		/*
+		 * Redirect stdout to stderr for the duration of the
+		 * metadump operation so that dbprintf and other messages
+		 * are sent to the console instead of polluting the
+		 * metadump stream.
+		 */
 		outf = stdout;
+		stdout = stderr;
+		stdout_metadump = true;
 	} else {
 		outf = fopen(argv[optind], "wb");
 		if (outf == NULL) {
@@ -3020,9 +3029,11 @@ 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 v2] xfs_db: redirect printfs when metadumping to stdout

[Carlos Maiolino]

On Sun, Jul 16, 2017 at 12:54:15PM -0700, 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>
> ---
> v2: Better comments.
> ---

Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>

>  db/metadump.c |   15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/db/metadump.c b/db/metadump.c
> index e046f60..b58acef 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;
> @@ -2988,7 +2989,15 @@ metadump_f(
>  			free(metablock);
>  			return 0;
>  		}
> +		/*
> +		 * Redirect stdout to stderr for the duration of the
> +		 * metadump operation so that dbprintf and other messages
> +		 * are sent to the console instead of polluting the
> +		 * metadump stream.
> +		 */
>  		outf = stdout;
> +		stdout = stderr;
> +		stdout_metadump = true;
>  	} else {
>  		outf = fopen(argv[optind], "wb");
>  		if (outf == NULL) {
> @@ -3020,9 +3029,11 @@ 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 */
> --
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-- 
Carlos