[PATCH] kvmtool: virtio-9p: Convert EMFILE error at the server to ENFILE for the guest

[PATCH] kvmtool: virtio-9p: Convert EMFILE error at the server to ENFILE for the guest

[Suzuki K. Poulose]

From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>

If an open at the 9p server(host) fails with EMFILE (Too many open files for
the process), we should return ENFILE(too many open files in the system) to
the guest to indicate the actual status within the guest.

This was uncovered during LTP, where getdtablesize01 fails to open the maximum
number-open-files.

getdtablesize01    0  TINFO  :  Maximum number of files a process can have opened is 1024
getdtablesize01    0  TINFO  :  Checking with the value returned by getrlimit...RLIMIT_NOFILE
getdtablesize01    1  TPASS  :  got correct dtablesize, value is 1024
getdtablesize01    0  TINFO  :  Checking Max num of files that can be opened by a process.Should be: RLIMIT_NOFILE - 1
getdtablesize01    2  TFAIL  :  getdtablesize01.c:102: 974 != 1023

For a more practial impact:

 # ./getdtablesize01 &
[1] 1834
 getdtablesize01    0  TINFO  :  Maximum number of files a process can have opened is 1024
 getdtablesize01    0  TINFO  :  Checking with the value returned by getrlimit...RLIMIT_NOFILE
 getdtablesize01    1  TPASS  :  got correct dtablesize, value is 1024
 getdtablesize01    0  TINFO  :  Checking Max num of files that can be opened by a process.Should be: RLIMIT_NOFILE - 1
 getdtablesize01    2  TFAIL  :  getdtablesize01.c:102: 974 != 1023
 [--- Modified to sleep indefinitely, without closing the files --- ]

 # ls
 bash: /bin/ls: Too many open files

That gives a wrong error message for the bash, when getdtablesize01 has exhausted the system
wide limits, giving false indicators.

With the fix, we get :

 # ls
 bash: /bin/ls: Too many open files in system

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
---
 tools/kvm/virtio/9p.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/kvm/virtio/9p.c b/tools/kvm/virtio/9p.c
index 9073a1e..b24c0f2 100644
--- a/tools/kvm/virtio/9p.c
+++ b/tools/kvm/virtio/9p.c
@@ -152,6 +152,10 @@ static void virtio_p9_error_reply(struct p9_dev *p9dev,
 {
 	u16 tag;
 
+	/* EMFILE at server implies ENFILE for the VM */
+	if (err == EMFILE)
+		err = ENFILE;
+
 	pdu->write_offset = VIRTIO_9P_HDR_LEN;
 	virtio_p9_pdu_writef(pdu, "d", err);
 	*outlen = pdu->write_offset;
-- 
1.7.9.5

Re: [PATCH] kvmtool: virtio-9p: Convert EMFILE error at the server to ENFILE for the guest

[Will Deacon]

On Fri, Jan 16, 2015 at 11:30:10AM +0000, Suzuki K. Poulose wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>
> 
> If an open at the 9p server(host) fails with EMFILE (Too many open files for
> the process), we should return ENFILE(too many open files in the system) to
> the guest to indicate the actual status within the guest.
> 
> This was uncovered during LTP, where getdtablesize01 fails to open the maximum
> number-open-files.
> 
> getdtablesize01    0  TINFO  :  Maximum number of files a process can have opened is 1024
> getdtablesize01    0  TINFO  :  Checking with the value returned by getrlimit...RLIMIT_NOFILE
> getdtablesize01    1  TPASS  :  got correct dtablesize, value is 1024
> getdtablesize01    0  TINFO  :  Checking Max num of files that can be opened by a process.Should be: RLIMIT_NOFILE - 1
> getdtablesize01    2  TFAIL  :  getdtablesize01.c:102: 974 != 1023
> 
> For a more practial impact:
> 
>  # ./getdtablesize01 &
> [1] 1834
>  getdtablesize01    0  TINFO  :  Maximum number of files a process can have opened is 1024
>  getdtablesize01    0  TINFO  :  Checking with the value returned by getrlimit...RLIMIT_NOFILE
>  getdtablesize01    1  TPASS  :  got correct dtablesize, value is 1024
>  getdtablesize01    0  TINFO  :  Checking Max num of files that can be opened by a process.Should be: RLIMIT_NOFILE - 1
>  getdtablesize01    2  TFAIL  :  getdtablesize01.c:102: 974 != 1023
>  [--- Modified to sleep indefinitely, without closing the files --- ]
> 
>  # ls
>  bash: /bin/ls: Too many open files
> 
> That gives a wrong error message for the bash, when getdtablesize01 has exhausted the system
> wide limits, giving false indicators.
> 
> With the fix, we get :
> 
>  # ls
>  bash: /bin/ls: Too many open files in system

I doubt this is affecting anybody in practice, but:

  Acked-by: Will Deacon <will.deacon@arm.com>

Will

> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
> ---
>  tools/kvm/virtio/9p.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/kvm/virtio/9p.c b/tools/kvm/virtio/9p.c
> index 9073a1e..b24c0f2 100644
> --- a/tools/kvm/virtio/9p.c
> +++ b/tools/kvm/virtio/9p.c
> @@ -152,6 +152,10 @@ static void virtio_p9_error_reply(struct p9_dev *p9dev,
>  {
>  	u16 tag;
>  
> +	/* EMFILE at server implies ENFILE for the VM */
> +	if (err == EMFILE)
> +		err = ENFILE;
> +
>  	pdu->write_offset = VIRTIO_9P_HDR_LEN;
>  	virtio_p9_pdu_writef(pdu, "d", err);
>  	*outlen = pdu->write_offset;
> -- 
> 1.7.9.5
>