kern: Add phashinit_flags(), which allows malloc(M_NOWAIT)

It will be used for the upcoming LRO hash table initialization.
And probably will be useful in other cases, when M_WAITOK can't
be used.

Reviewed by:	jhb, kib
Sponsored by:	Microsoft OSTC
Differential Revision:	https://reviews.freebsd.org/D6138

3 files changed, 46 insertions, 9 deletions

diff --git a/share/man/man9/hashinit.9 b/share/man/man9/hashinit.9
index 65ef10e..5357a95e 100644
--- a/share/man/man9/hashinit.9
+++ b/share/man/man9/hashinit.9
@@ -25,11 +25,11 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 23, 2016
+.Dd April 29, 2016
 .Dt HASHINIT 9
 .Os
 .Sh NAME
-.Nm hashinit , hashinit_flags , hashdestroy , phashinit
+.Nm hashinit , hashinit_flags ,  hashdestroy , phashinit , phashinit_flags
 .Nd manage kernel hash tables
 .Sh SYNOPSIS
 .In sys/malloc.h
@@ -45,12 +45,14 @@
 .Fn hashdestroy "void *hashtbl" "struct malloc_type *type" "u_long hashmask"
 .Ft "void *"
 .Fn phashinit "int nelements" "struct malloc_type *type" "u_long *nentries"
+.Fn phashinit_flags "int nelements" "struct malloc_type *type" "u_long *nentries" "int flags"
 .Sh DESCRIPTION
 The
 .Fn hashinit ,
-.Fn hashinit_flags
-and
+.Fn hashinit_flags ,
 .Fn phashinit
+and
+.Fn phashinit_flags
 functions allocate space for hash tables of size given by the argument
 .Fa nelements .
 .Pp
@@ -71,6 +73,12 @@ function operates like
 but also accepts an additional argument
 .Fa flags
 which control various options during allocation.
+.Fn phashinit_flags
+function operates like
+.Fn phashinit
+but also accepts an additional argument
+.Fa flags
+which control various options during allocation.
 Allocated hash tables are contiguous arrays of
 .Xr LIST_HEAD 3
 entries, allocated using
@@ -100,13 +108,19 @@ must be used with one of the following values.
 .It Dv HASH_NOWAIT
 Any malloc performed by the
 .Fn hashinit_flags
+and
+.Fn phashinit_flags
 function will not be allowed to wait, and therefore may fail.
 .It Dv HASH_WAITOK
 Any malloc performed by
 .Fn hashinit_flags
+and
+.Fn phashinit_flags
 function is allowed to wait for memory.
 This is also the behavior of
-.Fn hashinit .
+.Fn hashinit
+and
+.Fn phashinit .
 .El
 .Sh IMPLEMENTATION NOTES
 The largest prime hash value chosen by
diff --git a/sys/kern/subr_hash.c b/sys/kern/subr_hash.c
index 915f3f7..4d9249f 100644
--- a/sys/kern/subr_hash.c
+++ b/sys/kern/subr_hash.c
@@ -104,16 +104,21 @@ static const int primes[] = { 1, 13, 31, 61, 127, 251, 509, 761, 1021, 1531,
 #define	NPRIMES nitems(primes)
 
 /*
- * General routine to allocate a prime number sized hash table.
+ * General routine to allocate a prime number sized hash table with control of
+ * memory flags.
  */
 void *
-phashinit(int elements, struct malloc_type *type, u_long *nentries)
+phashinit_flags(int elements, struct malloc_type *type, u_long *nentries, int flags)
 {
 	long hashsize;
 	LIST_HEAD(generic, generic) *hashtbl;
-	int i;
+	int i, m_flags;
 
 	KASSERT(elements > 0, ("%s: bad elements", __func__));
+	/* Exactly one of HASH_WAITOK and HASH_NOWAIT must be set. */
+	KASSERT((flags & HASH_WAITOK) ^ (flags & HASH_NOWAIT),
+	    ("Bad flags (0x%x) passed to phashinit_flags", flags));
+
 	for (i = 1, hashsize = primes[1]; hashsize <= elements;) {
 		i++;
 		if (i == NPRIMES)
@@ -121,9 +126,25 @@ phashinit(int elements, struct malloc_type *type, u_long *nentries)
 		hashsize = primes[i];
 	}
 	hashsize = primes[i - 1];
-	hashtbl = malloc((u_long)hashsize * sizeof(*hashtbl), type, M_WAITOK);
+
+	m_flags = (flags & HASH_NOWAIT) ? M_NOWAIT : M_WAITOK;
+	hashtbl = malloc((u_long)hashsize * sizeof(*hashtbl), type, m_flags);
+	if (hashtbl == NULL)
+		return (NULL);
+
 	for (i = 0; i < hashsize; i++)
 		LIST_INIT(&hashtbl[i]);
 	*nentries = hashsize;
 	return (hashtbl);
 }
+
+/*
+ * Allocate and initialize a prime number sized hash table with default flag:
+ * may sleep.
+ */
+void *
+phashinit(int elements, struct malloc_type *type, u_long *nentries)
+{
+
+	return (phashinit_flags(elements, type, nentries, HASH_WAITOK));
+}
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index 34ad5ba..1f05f69 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -189,6 +189,8 @@ void	*hashinit_flags(int count, struct malloc_type *type,
 #define	HASH_WAITOK	0x00000002
 
 void	*phashinit(int count, struct malloc_type *type, u_long *nentries);
+void	*phashinit_flags(int count, struct malloc_type *type, u_long *nentries,
+    int flags);
 void	g_waitidle(void);
 
 void	panic(const char *, ...) __dead2 __printflike(1, 2);