When pstore was refactored to use the crypto compress API in:

  commit cb3bee0369bc ("pstore: Use crypto compress API")

nearly all the pstore-specific compression routines were replaced with
the existing crypto compression API. One case remained: calculating the
"worst case" compression sizes ahead of time so it could have a buffer
preallocated for doing compression (which was called "zbufsize").

To make pstore fully algorithm-agnostic, the compression API needs to
grow this functionality. This adds the interface to support querying the
"worst case" estimate, with a new "zbufsize" routine that each compressor
can implement. The per-compressor implementations come in later commits.

Signed-off-by: Kees Cook <redacted>
---
 crypto/compress.c                   |  9 +++++++++
 include/crypto/internal/scompress.h | 11 +++++++++++
 include/linux/crypto.h              | 12 ++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/crypto/compress.c b/crypto/compress.c
index f2d522924a07..29a80bb3b9d3 100644
--- a/crypto/compress.c
+++ b/crypto/compress.c

@@ -33,12 +33,21 @@ static int crypto_decompress(struct crypto_tfm *tfm,
 	                                                   dlen);
 }
 
+static int crypto_zbufsize(struct crypto_tfm *tfm,
+			   unsigned int slen, unsigned int *dlen)
+{
+	if (!tfm->__crt_alg->cra_compress.coa_zbufsize)
+		return -ENOTSUPP;
+	return tfm->__crt_alg->cra_compress.coa_zbufsize(tfm, slen, dlen);
+}