[PATCH] Use the reentrant getmntent_r instead of getmntent

[PATCH] Use the reentrant getmntent_r instead of getmntent

[Zhu Yanhai]

The function find_cgroup_mnt() could be called under multithread scenario, so
we should use the reentrant edition getmntent_r() instead of getmntent().

E.g, without this fix the output for below job file is wrong.

[root@localhost blkio-test]# cat small-read-file
[global]
ioengine=sync
direct=1
rw=read
bs=4k
filename=/dev/sdb
time_based
runtime=60
cgroup=small
cgroup_weight=500
numjobs=32
group_reporting
thread

[file1]

Then fio randomly says:
[cut here]
Starting 32 threads
fio: cgroup blkio does not appear to be mounted
fio: cgroup blkio does not appear to be mounted
fio: cgroup blkio does not appear to be mounted
---
 cgroup.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/cgroup.c b/cgroup.c
index f36683a..4f02ecd 100644
--- a/cgroup.c
+++ b/cgroup.c
@@ -22,7 +22,8 @@ struct cgroup_member {
 static char *find_cgroup_mnt(struct thread_data *td)
 {
 	char *mntpoint = NULL;
-	struct mntent *mnt;
+	struct mntent *mnt, dummy;
+	char buf[256] = {0};
 	FILE *f;
 
 	f = setmntent("/proc/mounts", "r");
@@ -31,7 +32,7 @@ static char *find_cgroup_mnt(struct thread_data *td)
 		return NULL;
 	}
 
-	while ((mnt = getmntent(f)) != NULL) {
+	while ((mnt = getmntent_r(f, &dummy, buf, 256)) != NULL) {
 		if (!strcmp(mnt->mnt_type, "cgroup") &&
 		    strstr(mnt->mnt_opts, "blkio"))
 			break;
-- 
1.7.4.4

Re: [PATCH] Use the reentrant getmntent_r instead of getmntent

[Jens Axboe]

On 2011-11-22 07:56, Zhu Yanhai wrote:
> The function find_cgroup_mnt() could be called under multithread scenario, so
> we should use the reentrant edition getmntent_r() instead of getmntent().
> 
> E.g, without this fix the output for below job file is wrong.
> 
> [root@localhost blkio-test]# cat small-read-file
> [global]
> ioengine=sync
> direct=1
> rw=read
> bs=4k
> filename=/dev/sdb
> time_based
> runtime=60
> cgroup=small
> cgroup_weight=500
> numjobs=32
> group_reporting
> thread
> 
> [file1]
> 
> Then fio randomly says:
> [cut here]
> Starting 32 threads
> fio: cgroup blkio does not appear to be mounted
> fio: cgroup blkio does not appear to be mounted
> fio: cgroup blkio does not appear to be mounted
> ---
>  cgroup.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/cgroup.c b/cgroup.c
> index f36683a..4f02ecd 100644
> --- a/cgroup.c
> +++ b/cgroup.c
> @@ -22,7 +22,8 @@ struct cgroup_member {
>  static char *find_cgroup_mnt(struct thread_data *td)
>  {
>  	char *mntpoint = NULL;
> -	struct mntent *mnt;
> +	struct mntent *mnt, dummy;
> +	char buf[256] = {0};
>  	FILE *f;
>  
>  	f = setmntent("/proc/mounts", "r");
> @@ -31,7 +32,7 @@ static char *find_cgroup_mnt(struct thread_data *td)
>  		return NULL;
>  	}
>  
> -	while ((mnt = getmntent(f)) != NULL) {
> +	while ((mnt = getmntent_r(f, &dummy, buf, 256)) != NULL) {
>  		if (!strcmp(mnt->mnt_type, "cgroup") &&
>  		    strstr(mnt->mnt_opts, "blkio"))
>  			break;

Thanks applied, with a small change to use sizeof(buf) instead of 256 in
both places.

-- 
Jens Axboe