[PATCH] crypto: relocate ALG_MAX_PAGES to uapi

[PATCH] crypto: relocate ALG_MAX_PAGES to uapi

[Stephan Mueller]

The define of ALG_MAX_PAGES is relevant for user space as this macro
defines the maximum number of pages to be processed in one go by
vmsplice/splice. If user space does not obey that limit, the calling
thread will hang until a recvmsg is called (by another thread).

As user space should have the ability to prevent such blocks, it needs
to know about the limit. Therefore, the define is moved to the uapi
header file.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 include/crypto/if_alg.h     | 2 --
 include/uapi/linux/if_alg.h | 3 +++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index 018afb2..fb00376 100644
--- a/include/crypto/if_alg.h
+++ b/include/crypto/if_alg.h
@@ -20,8 +20,6 @@
 #include <linux/types.h>
 #include <net/sock.h>
 
-#define ALG_MAX_PAGES			16
-
 struct crypto_async_request;
 
 struct alg_sock {
diff --git a/include/uapi/linux/if_alg.h b/include/uapi/linux/if_alg.h
index f2acd2f..96af72f 100644
--- a/include/uapi/linux/if_alg.h
+++ b/include/uapi/linux/if_alg.h
@@ -39,4 +39,7 @@ struct af_alg_iv {
 #define ALG_OP_DECRYPT			0
 #define ALG_OP_ENCRYPT			1
 
+/* Maximum number of pages to be processed */
+#define ALG_MAX_PAGES			16
+
 #endif	/* _LINUX_IF_ALG_H */
-- 
2.5.0

Re: [PATCH] crypto: relocate ALG_MAX_PAGES to uapi

[Herbert Xu]

On Fri, Dec 25, 2015 at 06:14:54PM +0100, Stephan Mueller wrote:
> The define of ALG_MAX_PAGES is relevant for user space as this macro
> defines the maximum number of pages to be processed in one go by
> vmsplice/splice. If user space does not obey that limit, the calling
> thread will hang until a recvmsg is called (by another thread).
> 
> As user space should have the ability to prevent such blocks, it needs
> to know about the limit. Therefore, the define is moved to the uapi
> header file.
> 
> Signed-off-by: Stephan Mueller <smueller@chronox.de>

I don't like exporting details like this.  User-space should not
be relying on voodoo like this to avoid hanging.

Please show me the program that actually hangs so we can figure
out what if anything needs to be done to address this.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt