path: root/share/man/man9/malloc.9

.\"	$OpenBSD: malloc.9,v 1.67 2019/02/07 15:11:38 visa Exp $
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.Dd $Mdocdate: February 7 2019 $
.Dt MALLOC 9
.Os
.Sh NAME
.Nm malloc ,
.Nm mallocarray ,
.Nm free
.Nd kernel memory allocator
.Sh SYNOPSIS
.In sys/types.h
.In sys/malloc.h
.Ft void *
.Fn malloc "size_t size" "int type" "int flags"
.Ft void *
.Fn mallocarray "size_t nmemb" "size_t size" "int type" "int flags"
.Ft void
.Fn free "void *addr" "int type" "size_t size"
.Sh DESCRIPTION
The
.Fn malloc
function allocates uninitialized memory in kernel address space for an
object whose size is specified by
.Fa size .
.Pp
The
.Fn mallocarray
function is the same as
.Fn malloc ,
but allocates space for an array of
.Fa nmemb
objects and checks for arithmetic overflow.
.Pp
The
.Fn free
function releases memory at address
.Fa addr
that was previously allocated by
.Fn malloc
or
.Fn mallocarray
for re-use.
The same object size originally provided to
.Fn malloc
should be specified by
.Fa size ,
because
.Fn free
will operate faster knowing this.
If tracking the size is difficult, specify
.Ar size
as 0.
If
.Fa addr
is a null pointer, no action occurs.
.Pp
The
.Fa flags
argument affects the operational characteristics of
.Fn malloc
and
.Fn mallocarray
as follows:
.Bl -tag -width xxx -offset indent
.It Dv M_WAITOK
If memory is currently unavailable,
.Fn malloc
may call sleep to wait for resources to be released by other processes.
.It Dv M_NOWAIT
Causes
.Fn malloc
to return
.Dv NULL
if the request cannot be immediately fulfilled due to resource shortage.
.It Dv M_CANFAIL
In the
.Dv M_WAITOK
case, if not enough memory is available, return
.Dv NULL
instead of calling
.Xr panic 9 .
If
.Fn mallocarray
detects an overflow
or
.Fn malloc
detects an excessive allocation, return
.Dv NULL
instead of calling
.Xr panic 9 .
.It Dv M_ZERO
Causes allocated memory to be zeroed.
.El
.Pp
One of
.Dv M_NOWAIT
or
.Dv M_WAITOK
must be specified via the
.Fa flags
argument.
.Pp
The
.Fa type
argument broadly identifies the kernel subsystem for which the allocated
memory was needed, and is commonly used to maintain statistics about
kernel memory usage.
These statistics can be examined using
.Xr vmstat 8
or
.Xr systat 1
if either of the kernel
.Xr options 4
.Cm KMEMSTATS
or
.Cm DEBUG
are enabled.
.Pp
The following types are currently defined:
.Pp
.Bl -tag -offset indent -width XXXXXXXXXXXXXX -compact
.It Dv M_FREE
Should be on free list.
.It Dv M_DEVBUF
Device driver memory.
.It Dv M_PCB
Protocol control blocks.
.It Dv M_RTABLE
Routing tables.
.It Dv M_IFADDR
Interface addresses.
.It Dv M_SOOPTS
Socket options.
.It Dv M_SYSCTL
Sysctl persistent buffers.
.It Dv M_COUNTERS
Per-CPU Counters for use via
.Xr counters_alloc 9 .
.It Dv M_IOCTLOPS
Ioctl data buffers.
.It Dv M_IOV
Large IOVs.
.It Dv M_MOUNT
VFS mount structs.
.It Dv M_NFSREQ
NFS request headers.
.It Dv M_NFSMNT
NFS mount structures.
.It Dv M_VNODE
Dynamically allocated vnodes.
.It Dv M_CACHE
Dynamically allocated cache entries.
.It Dv M_DQUOT
UFS quota entries.
.It Dv M_UFSMNT
UFS mount structures.
.It Dv M_SHM
SVID compatible shared memory segments.
.It Dv M_VMMAP
VM map structures.
.It Dv M_SEM
SVID compatible semaphores.
.It Dv M_DIRHASH
UFS directory hash structures.
.It Dv M_ACPI
ACPI structures.
.It Dv M_VMPMAP
VM pmap data.
.It Dv M_FILE
Open file structures.
.It Dv M_FILEDESC
Open file descriptor tables.
.It Dv M_SIGIO
Sigio structures.
.It Dv M_PROC
Proc structures.
.It Dv M_SUBPROC
Proc sub-structures.
.It Dv M_VCLUSTER
Cluster for VFS.
.It Dv M_MFSNODE
MFS vnode private part.
.It Dv M_NETADDR
Export host address structures.
.It Dv M_NFSSVC
NFS server structures.
.It Dv M_NFSD
NFS server daemon structures.
.It Dv M_IPMOPTS
Internet multicast options.
.It Dv M_IPMADDR
Internet multicast addresses.
.It Dv M_IFMADDR
Link-level multicast addresses.
.It Dv M_MRTABLE
Multicast routing tables.
.It Dv M_ISOFSMNT
ISOFS mount structures.
.It Dv M_ISOFSNODE
ISOFS vnode private part.
.It Dv M_MSDOSFSMNT
MSDOS FS mount structures.
.It Dv M_MSDOSFSFAT
MSDOS FS FAT tables.
.It Dv M_MSDOSFSNODE
MSDOS FS vnode private part.
.It Dv M_TTYS
Allocated tty structures.
.It Dv M_EXEC
Argument lists & other mem used by exec.
.It Dv M_MISCFSMNT
Miscellaneous FS mount structures.
.It Dv M_FUSEFS
FUSE FS mount structures.
.It Dv M_PFKEY
Pfkey data.
.It Dv M_TDB
Transforms database.
.It Dv M_XDATA
IPsec data.
.It Dv M_PAGEDEP
File page dependencies.
.It Dv M_INODEDEP
Inode dependencies.
.It Dv M_NEWBLK
New block allocation.
.It Dv M_INDIRDEP
Indirect block dependencies.
.It Dv M_VMSWAP
VM swap structures.
.It Dv M_UVMAMAP
UVM amap and related.
.It Dv M_UVMAOBJ
UVM aobj and related.
.It Dv M_USB
USB general.
.It Dv M_USBDEV
USB device driver.
.It Dv M_USBHC
USB host controller.
.It Dv M_WITNESS
.Xr witness 4
memory.
.It Dv M_MEMDESC
Memory range.
.It Dv M_CRYPTO_DATA
.Xr crypto 9
data buffers.
.It Dv M_CREDENTIALS
.Xr ipsec 4
related credentials.
.It Dv M_EMULDATA
Per process emulation data.
.It Dv M_IP6OPT
IPv6 options.
.It Dv M_IP6NDP
IPv6 neighbour discovery structures.
.It Dv M_TEMP
Miscellaneous temporary data buffers.
.It Dv M_NTFSMNT
NTFS mount structures.
.It Dv M_NTFSNTNODE
NTFS ntnode information.
.It Dv M_NTFSFNODE
NTFS fnode information.
.It Dv M_NTFSDIR
NTFS directory buffers.
.It Dv M_NTFSNTHASH
NTFS ntnode hash tables.
.It Dv M_NTFSNTVATTR
NTFS file attribute information.
.It Dv M_NTFSRDATA
NTFS resident data.
.It Dv M_NTFSDECOMP
NTFS decompression temporary storage.
.It Dv M_NTFSRUN
NTFS vrun storage.
.It Dv M_KEVENT
.Xr kqueue 2
data structures.
.It Dv M_SYNCACHE
SYN cache hash array.
.It Dv M_UDFMOUNT
UDF mount structures.
.It Dv M_UDFFENTRY
UDF file entries.
.It Dv M_UDFFID
UDF file ID.
.It Dv M_AGP
AGP memory.
.It Dv M_DRM
Direct Rendering Manager.
.El
.Sh CONTEXT
.Fn malloc
and
.Fn mallocarray
can be called during autoconf, from process context, or from interrupt context
if
.Dv M_NOWAIT
is passed via
.Fa flags .
They can't be called from interrupt context if
.Dv M_WAITOK
is passed via
.Fa flags .
.Pp
.Fn free
can be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Fn malloc
and
.Fn mallocarray
return a kernel virtual address that is suitably aligned for storage of
any type of object.
.Sh DIAGNOSTICS
A kernel compiled with the
.Dv DIAGNOSTIC
configuration option attempts to detect memory corruption caused by
such things as writing outside the allocated area and unbalanced calls to
.Fn malloc
or
.Fn mallocarray ,
and
.Fn free .
Failing consistency checks will cause a panic or a system console message:
.Pp
.Bl -bullet -offset indent -compact
.It
panic:
.Dq malloc: bogus type
.It
panic:
.Dq malloc: out of space in kmem_map
.It
panic:
.Dq malloc: allocation too large
.It
panic:
.Dq malloc: wrong bucket
.It
panic:
.Dq malloc: lost data
.It
panic:
.Dq mallocarray: overflow
.It
panic:
.Dq free: unaligned addr
.It
panic:
.Dq free: duplicated free
.It
panic:
.Dq free: multiple frees
.It
panic:
.Dq free: non-malloced addr
.It
panic:
.Dq free: size too large
.It
panic:
.Dq free: size too small
.It
panic:
.Dq kmeminit: minbucket too small/struct freelist too big
.It
.Dq multiply freed item Aq addr
.It
.Dq Data modified on freelist: Aq data object description
.El
.Sh SEE ALSO
.Xr systat 1 ,
.Xr vmstat 8