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Diffstat (limited to 'Documentation/crypto')
| -rw-r--r-- | Documentation/crypto/userspace-if.rst | 31 |
1 files changed, 4 insertions, 27 deletions
diff --git a/Documentation/crypto/userspace-if.rst b/Documentation/crypto/userspace-if.rst index 021759198fe7..d220e266b8de 100644 --- a/Documentation/crypto/userspace-if.rst +++ b/Documentation/crypto/userspace-if.rst @@ -327,33 +327,10 @@ CRYPTO_USER_API_RNG_CAVP option: Zero-Copy Interface ------------------- -In addition to the send/write/read/recv system call family, the AF_ALG -interface can be accessed with the zero-copy interface of -splice/vmsplice. As the name indicates, the kernel tries to avoid a copy -operation into kernel space. - -The zero-copy operation requires data to be aligned at the page -boundary. Non-aligned data can be used as well, but may require more -operations of the kernel which would defeat the speed gains obtained -from the zero-copy interface. - -The system-inherent limit for the size of one zero-copy operation is 16 -pages. If more data is to be sent to AF_ALG, user space must slice the -input into segments with a maximum size of 16 pages. - -Zero-copy can be used with the following code example (a complete -working example is provided with libkcapi): - -:: - - int pipes[2]; - - pipe(pipes); - /* input data in iov */ - vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT); - /* opfd is the file descriptor returned from accept() system call */ - splice(pipes[0], NULL, opfd, NULL, ret, 0); - read(opfd, out, outlen); +AF_ALG used to have zero-copy support, but it was removed due to it being a +frequent source of vulnerabilities. For backwards compatibility the splice() +and sendfile() system calls are still supported, but the kernel will make an +internal copy of the data before passing it to the crypto code. Setsockopt Interface |