Re: [PATCH 1/1] mount.nfs: mtab corruption when RLIMIT_FSIZE causes a partial write

[Jeff Layton <jlayton@poochiereds.net>]

On Wed, 19 Oct 2011 11:34:30 -0400
Steve Dickson <steved@redhat.com> wrote:

> This patch is a following on to commit 7a802337. Using the
> tool in https://bugzilla.redhat.com/show_bug.cgi?id=695916
> caused the fflush() and fclose() to fail in turn causing
> corruption in the mtab.
> 
> The failures were in the internals of both calls. Switch those
> calls with the actual system calls eliminated the failures.
> 
> Signed-off-by: Steve Dickson <steved@redhat.com>
> ---
>  support/nfs/nfs_mntent.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/support/nfs/nfs_mntent.c b/support/nfs/nfs_mntent.c
> index a2118a2..b80f270 100644
> --- a/support/nfs/nfs_mntent.c
> +++ b/support/nfs/nfs_mntent.c
> @@ -117,7 +117,7 @@ void
>  nfs_endmntent (mntFILE *mfp) {
>  	if (mfp) {
>  		if (mfp->mntent_fp)
> -			fclose(mfp->mntent_fp);
> +			close(fileno(mfp->mntent_fp));
>  		if (mfp->mntent_file)
>  			free(mfp->mntent_file);
>  		free(mfp);
> @@ -147,7 +147,7 @@ nfs_addmntent (mntFILE *mfp, struct mntent *mnt) {
>  	free(m3);
>  	free(m4);
>  	if (res >= 0) {
> -		res = fflush(mfp->mntent_fp);
> +		res = fsync(fileno(mfp->mntent_fp));

fsync doesn't imply an fflush. With this, I think you may end up
without everything being committed to disk if part or all of it is
still in the file stream buffer. You probably want to do an fflush()
and then an fsync here.

>  		if (res < 0)
>  			/* Avoid leaving a corrupt mtab file */
>  			ftruncate(fileno(mfp->mntent_fp), length);


-- 
Jeff Layton <jlayton@poochiereds.net>