Re: [PATCH v2] nfs-utils: Increase the stdio file buffer size for procfs files

["J. Bruce Fields" <bfields@fieldses.org>]

Looks sensible to me.--b.

On Fri, Apr 08, 2011 at 01:16:46PM +0200, Sean Finney wrote:
> Previously, when writing to /proc/net/rpc/*/channel, if a cache line
> were larger than the default buffer size (likely 1024 bytes), mountd
> and svcgssd would split writes into a number of buffer-sized writes.
> Each of these writes would get an EINVAL error back from the kernel
> procfs handle (it expects line-oriented input and does not account for
> multiple/split writes), and no cache update would occur.
> 
> When such behavior occurs, NFS clients depending on mountd to finish
> the cache operation would block/hang, or receive EPERM, depending on
> the context of the operation.  This is likely to happen if a user is a
> member of a large (~100-200) number of groups.
> 
> Instead, every fopen() on the procfs files in question is followed by
> a call to setvbuf(), using a per-file dedicated buffer of
> RPC_CHAN_BUF_SIZE length.
> 
> Really, mountd should not be using stdio-style buffered file operations
> on files in /proc to begin with.  A better solution would be to use
> internally managed buffers and calls to write() instead of these stdio
> calls, but that would be a more extensive change; so this is proposed
> as a quick and not-so-dirty fix in the meantime.
> 
> Signed-off-by: Sean Finney <sean.finney@sonyericsson.com>
> ---
>  support/include/misc.h    |    3 +++
>  utils/gssd/svcgssd_proc.c |    3 +++
>  utils/mountd/cache.c      |    2 ++
>  3 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/support/include/misc.h b/support/include/misc.h
> index 9a1b25d..7e3874e 100644
> --- a/support/include/misc.h
> +++ b/support/include/misc.h
> @@ -24,4 +24,7 @@ struct hostent *get_reliable_hostbyaddr(const char *addr, int len, int type);
>  
>  extern int is_mountpoint(char *path);
>  
> +/* size of the file pointer buffers for rpc procfs files */
> +#define RPC_CHAN_BUF_SIZE 32768
> +
>  #endif /* MISC_H */
> diff --git a/utils/gssd/svcgssd_proc.c b/utils/gssd/svcgssd_proc.c
> index 6f2ba61..8f6548e 100644
> --- a/utils/gssd/svcgssd_proc.c
> +++ b/utils/gssd/svcgssd_proc.c
> @@ -56,6 +56,7 @@
>  #include "gss_util.h"
>  #include "err_util.h"
>  #include "context.h"
> +#include "misc.h"
>  
>  extern char * mech2file(gss_OID mech);
>  #define SVCGSSD_CONTEXT_CHANNEL "/proc/net/rpc/auth.rpcsec.context/channel"
> @@ -78,6 +79,7 @@ do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
>  	FILE *f;
>  	int i;
>  	char *fname = NULL;
> +	char vbuf[RPC_CHAN_BUF_SIZE];
>  	int err;
>  
>  	printerr(1, "doing downcall\n");
> @@ -90,6 +92,7 @@ do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
>  			     SVCGSSD_CONTEXT_CHANNEL, strerror(errno));
>  		goto out_err;
>  	}
> +	setvbuf(f, vbuf, _IOLBF, RPC_CHAN_BUF_SIZE);
>  	qword_printhex(f, out_handle->value, out_handle->length);
>  	/* XXX are types OK for the rest of this? */
>  	/* For context cache, use the actual context endtime */
> diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> index 34808cd..bd67157 100644
> --- a/utils/mountd/cache.c
> +++ b/utils/mountd/cache.c
> @@ -739,6 +739,7 @@ struct {
>  	char *cache_name;
>  	void (*cache_handle)(FILE *f);
>  	FILE *f;
> +	char vbuf[RPC_CHAN_BUF_SIZE];
>  } cachelist[] = {
>  	{ "auth.unix.ip", auth_unix_ip},
>  	{ "auth.unix.gid", auth_unix_gid},
> @@ -757,6 +758,7 @@ void cache_open(void)
>  			continue;
>  		sprintf(path, "/proc/net/rpc/%s/channel", cachelist[i].cache_name);
>  		cachelist[i].f = fopen(path, "r+");
> +		setvbuf(cachelist[i].f, cachelist[i].vbuf, _IOLBF, RPC_CHAN_BUF_SIZE);
>  	}
>  }
>  
> -- 
> 1.7.4.1
> 
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