Created attachment 577350 [details]
patch for utils/mountd/cache.c

Description of problem:

On our file server cluster we have many exports with individual netgroups. On some clients it is not possible to mount some shares. What we get is the following error message on the server:

Apr 12 12:04:22 srv rpc.mountd[12143]: qword_printhex: fwrite failed: errno 22 (Invalid argument)
Apr 12 12:04:22 srv rpc.mountd[12143]: qword_eol: fflush failed: errno 22 (Invalid argument)
Apr 12 12:04:22 srv rpc.mountd[12143]: Cannot export /export/..., possibly unsupported filesystem or fsid= required

We have tracked down the problem to this commit which is missing in the
nfs-utils in RHEL 6.2:

  http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=commitdiff;h=5604b35a61e22930873ffc4e9971002f578e7978

This patch alone does not solve the problem though. The two functions
cache_export() and cache_export_ent() in utils/mountd/cache.c must also
be modified to get a larger buffer via setvbuf(). A patch is attached to
this report.

Version-Release number of selected component (if applicable):

nfs-utils-1.2.3-15.el6.x86_64

The additional patch is not present in upstream and should probably be added there too.

Additional info:

The reason why this is triggered at our site is similar to the one of the following bug I reported against RHEL4 long ago here: 

   https://lkml.org/lkml/2007/7/30/116

Basically rpc.mountd builds a long string with netgroups and the first
1024 bytes of the incomplete string are flushed by stdio:

12295 open("/proc/net/rpc/auth.unix.ip/channel", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 12
12295 fstat(12, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
12295 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ffabf567000
12295 write(12, "nfsd x.x.x.x 1334318187 *,@aadiya,@akourtis,@akreutz,@aligma,@alonso,@amamin,@amarfurt,@amoga,@antoinek,@asinghan,@azachary,@azala,@baslergi,@baumanan,@baumanmo,@bcagri,@blukas,@brams,@briangol,@"..., 1024) = -1 EINVAL (Invalid argument)
12295 sendto(11, "<28>Apr 13 13:26:27 rpc.mountd[12295]: qword_print: fwrite failed: errno 22 (Invalid argument)", 94, MSG_NOSIGNAL, NULL, 0) = 94
12295 write(12, "\n", 1)                = -1 EINVAL (Invalid argument)
12295 sendto(11, "<28>Apr 13 13:26:27 rpc.mountd[12295]: qword_eol: fflush failed: errno 22 (Invalid argument)", 92, MSG_NOSIGNAL, NULL, 0) = 92
12295 close(12)                         = 0