ref: 75c92428225428c8fde2d015f010e608a0b12f1d
dir: purgatorio/man/10/xalloc
.TH XALLOC 10.2 .SH NAME xalloc, xspanalloc, xfree \- basic memory management .SH SYNOPSIS .ta \w'\fLvoid* 'u .B void* xalloc(ulong size) .PP .B void* xspanalloc(ulong size, int align, ulong span) .PP .B void xfree(void *p) .SH DESCRIPTION .I Xalloc and .I xfree are primitives used by higher-level memory allocators in the kernel, such as .IR malloc (10.2). They are not intended for use directly by most kernel routines. The main exceptions are routines that permanently allocate large structures, or need the special alignment properties guaranteed by .IR xspanalloc . .PP .I Xalloc returns a pointer to a range of size bytes of memory. The memory will be zero filled and aligned on a 8 byte .RB ( BY2V ) address. If the memory is not available, .B xalloc returns a null pointer. .PP .I Xspanalloc allocates memory given alignment and spanning constraints. The block returned will contain .I size bytes, aligned on a boundary that is .BI "0 mod" " align," in such a way that the memory in the block does not span an address that is .BI "0 mod" " span." .I Xspanalloc is intended for use allocating hardware data structures (eg, page tables) or I/O buffers that must satisfy specific alignment restrictions. If .I xspanalloc cannot allocate memory to satisfy the given constraints, it will .IR panic (10.2). The technique it uses can sometimes cause memory to be wasted. Consequently, .I xspanalloc should be used sparingly. .PP .I Xfree frees the block of memory at .IR p , which must be an address previously returned by .I xalloc (not .IR xspanalloc ). .SS Allocation status Some memory allocation statistics are written to the console in response to the debugging sequence .LR "control-T control-T x" . The output includes the total free space, the number of free holes, and a summary of active holes. Each line shows `address top size'. .SH SEE ALSO .IR malloc (10.2)