MALLOC(9) NetBSD Kernel Manual MALLOC(9)
NAME
malloc, free - kernel memory allocator
SYNOPSIS
void * malloc(unsigned long size, int type, int flags); MALLOC(space, cast, unsigned long size, int type, int flags); void free(void *addr, int type); FREE(void *addr, int type);
DESCRIPTION
The malloc() function allocates uninitialized memory in kernel address space for an object whose size is specified by size. free() releases memory at address addr that was previously allocated by malloc() for re- use. The MALLOC() macro variant is functionally equivalent to (space) = (cast)malloc((u_long)(size), type, flags) and the FREE() macro variant is equivalent to free((caddr_t)(addr), type) Unlike its standard C library counterpart (malloc(3)), the kernel version takes two more arguments. The flags argument further qualifies malloc()'s operational charateristics as follows: M_NOWAIT Causes malloc() to return NULL if the request cannot be immedi- ately fulfilled due to resource shortage. Otherwise, malloc() may call sleep to wait for resources to be released by other pro- cesses. If this flag is not set, malloc() will never return NULL. Note that M_WAITOK is conveniently defined to be 0, and hence maybe or'ed into the flags argument to indicate that it's Ok to wait for resources. Currently, only one flag is defined. The 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. The following types are currently defined: M_FREE Should be on free list. M_MBUF Mbuf memory. M_DEVBUF Device driver memory. M_SOCKET Socket structure. M_PCB Protocol control block. M_RTABLE Routing tables. M_HTABLE IMP host tables. M_FTABLE Fragment reassembly header. M_ZOMBIE Zombie proc status M_IFADDR Interface address. M_SOOPTS Socket options. M_SONAME Socket name. M_NAMEI Namei path name buffer. M_GPROF Kernel profiling buffer. M_IOCTLOPS Ioctl data buffer. M_MAPMEM Mapped memory descriptors. M_CRED Credentials. M_PGRP Process group header. M_SESSION Session header. M_IOV Large iov's. M_MOUNT Vfs mount struct. M_FHANDLE Network file handle. M_NFSREQ NFS request header. M_NFSMNT NFS mount structure. M_NFSNODE NFS vnode private part. M_VNODE Dynamically allocated vnodes. M_CACHE Dynamically allocated cache entries. M_DQUOT UFS quota entries. M_UFSMNT UFS mount structure. M_SHM SVID compatible shared memory segments. M_VMMAP VM map structures. M_VMMAPENT VM map entry structures. M_VMOBJ VM object structure. M_VMOBJHASH VM object hash structure. M_VMPMAP VM pmap. M_VMPVENT VM phys-virt mapping entry. M_VMPAGER XXX: VM pager struct. M_VMPGDATA XXX: VM pager private data. M_FILE Open file structure. M_FILEDESC Open file descriptor table. M_LOCKF Byte-range locking structures. M_PROC Proc structures. M_SUBPROC Proc sub-structures. M_SEGMENT Segment for LFS. M_LFSNODE LFS vnode private part. M_FFSNODE FFS vnode private part. M_MFSNODE MFS vnode private part. M_NQLEASE Nqnfs lease. M_NQMHOST Nqnfs host address table. M_NETADDR Export host address structure. M_NFSSVC Nfs server structure. M_NFSUID Nfs uid mapping structure. M_NFSD Nfs server daemon structure. M_IPMOPTS Internet multicast options. M_IPMADDR Internet multicast address. M_IFMADDR Link-level multicast address. M_MRTABLE Multicast routing tables. M_ISOFSMNT ISOFS mount structure. M_ISOFSNODE ISOFS vnode private part. M_MSDOSFSMNT MSDOS FS mount structure. M_MSDOSFSFAT MSDOS FS fat table. M_MSDOSFSNODE MSDOS FS vnode private part. M_TTYS Allocated tty structures. M_EXEC Argument lists & other mem used by exec. M_MISCFSMNT Miscfs mount structures. M_MISCFSNODE Miscfs vnode private part. M_ADOSFSMNT Adosfs mount structures. M_ADOSFSNODE Adosfs vnode private part. M_ANODE Adosfs anode structures and tables. M_IPQ IP packet queue entry. M_AFS Andrew File System. M_ADOSFSBITMAP Adosfs bitmap. M_NFSSRVDESC NFS server descriptor. M_NFSDIROFF NFS directory cookies. M_NFSBIGFH NFS big filehandle. M_EXT2FSNODE EXT2FS vnode private part. M_VMSWAP VM swap structures. M_VMPAGE VM page structures. M_VMPBUCKET VM page buckets. M_UVMAMAP UVM amap and related structs. M_UVMAOBJ UVM aobj and related structs. M_DMAMAP bus_dma(9) structures. M_IPFLOW IP flow entries. M_USB USB general. M_USBDEV USB permanent. M_POOL Memory pool(9) structures. M_CFS Coda file system structures and tables. M_TEMP Misc temporary data buffers. Statistics based on the type argument is maintained only if the kernel option KMEMSTATS is used when compiling the kernel (the default in currentNetBSD kernels) and can be examined by using `vmstat -m'.
RETURN VALUES
malloc() returns a kernel virtual address that is suitably aligned for storage of any type of object.
SEE ALSO
vmstat(8)
DIAGNOSTICS
A kernel compiled with the DIAGNOSTIC configuration option attempts to detect detect memory corruption caused by such things as writing outside the allocated area and imbalanced calls to the malloc() and free() func- tions. Failing consistency checks will cause a panic or a system console message: + panic: ``malloc - bogus type'' + panic: ``malloc: out of space in kmem_map'' + panic: ``malloc: allocation too large'' + panic: ``malloc: wrong bucket'' + panic: ``malloc: lost data'' + panic: ``free: unaligned addr'' + panic: ``free: duplicated free'' + panic: ``free: multiple frees'' + panic: ``init: minbucket too small/struct freelist too big'' + ``multiply freed item <addr>'' + ``Data modified on freelist: <data object description>'' NetBSD 1.4 June 16, 1996 3
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