Re: [Libguestfs] [PATCH nbdkit v2 3/4] common/utils: Add vector_reserve_page_aligned

Allow vectors to be page aligned (eg. for performance or page protection reasons). To create a page aligned vector you have to use <vector>_reserve_page_aligned instead of plain <vector>_reserve. Note that <vector>_duplicate creates unaligned duplicates. --- configure.ac | 4 ++- common/utils/vector.h | 12 +++++++ common/utils/vector.c | 82 +++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 94 insertions(+), 4 deletions(-) diff --git a/configure.ac b/configure.ac index c426aec8..1ab85e3e 100644 --- a/configure.ac +++ b/configure.ac @@ -384,7 +384,9 @@ AC_CHECK_FUNCS([\ pipe \ pipe2 \ ppoll \ - posix_fadvise]) + posix_fadvise \ + posix_memalign \ + valloc]) dnl Check for structs and members. AC_CHECK_MEMBERS([struct dirent.d_type], [], [], [[#include <dirent.h>]]) diff --git a/common/utils/vector.h b/common/utils/vector.h index 1d04f812..50dd895d 100644 --- a/common/utils/vector.h +++ b/common/utils/vector.h @@ -101,6 +101,15 @@ sizeof (type)); \ } \ \ + /* Same as _reserve, but the allocation will be page aligned. \ + */ \ + static inline int \ + name##_reserve_page_aligned (name *v, size_t n) \ + { \ + return generic_vector_reserve_page_aligned ((struct generic_vector *)v, \ + n, sizeof (type)); \ + } \ + \ /* Insert at i'th element. i=0 => beginning i=len => append */ \ static inline int \ name##_insert (name *v, type elem, size_t i) \ @@ -197,4 +206,7 @@ struct generic_vector { extern int generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize); +extern int generic_vector_reserve_page_aligned (struct generic_vector *v, + size_t n, size_t itemsize); + #endif /* NBDKIT_VECTOR_H */ diff --git a/common/utils/vector.c b/common/utils/vector.c index 54e6b810..8f0c33b1 100644 --- a/common/utils/vector.c +++ b/common/utils/vector.c @@ -34,15 +34,17 @@ #include <stdio.h> #include <stdlib.h> +#include <unistd.h> #include <errno.h> +#include <assert.h> #include "checked-overflow.h" #include "vector.h" -int -generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) +static int +calculate_capacity (struct generic_vector *v, size_t n, size_t itemsize, + size_t *newcap_r, size_t *newbytes_r) { - void *newptr; size_t reqcap, reqbytes, newcap, newbytes, t; /* New capacity requested. We must allocate this minimum (or fail). @@ -71,6 +73,20 @@ generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) newbytes = reqbytes; } + *newcap_r = newcap; + *newbytes_r = newbytes; + return 0; +} + +int +generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) +{ + void *newptr; + size_t newcap, newbytes; + + if (calculate_capacity (v, n, itemsize, &newcap, &newbytes) == -1) + return -1; + newptr = realloc (v->ptr, newbytes); if (newptr == NULL) return -1; @@ -79,3 +95,63 @@ generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) v->cap = newcap; return 0; } + +/* Always allocates a buffer which is page aligned (both base and size). */ +int +generic_vector_reserve_page_aligned (struct generic_vector *v, + size_t n, size_t itemsize) +{ +#ifdef HAVE_POSIX_MEMALIGN + int r; +#endif + void *newptr; + size_t newcap, newbytes; + long pagesize; + size_t extra, extra_items; + + pagesize = sysconf (_SC_PAGE_SIZE); + assert (pagesize > 0); + + if (calculate_capacity (v, n, itemsize, &newcap, &newbytes) == -1) + return -1; + + /* If the new size (in bytes) is not a full page then we have to + * round up to the next page. Note we make the implicit assumption + * here that itemsize is divisible by pagesize, but I assume you

+ * know what you're doing if you're using this function. + */ + extra = newbytes & (pagesize - 1);

+ if (extra > 0) { + extra_items = (pagesize - extra) / itemsize;

+ + if (ADD_OVERFLOW (newcap, extra_items, &newcap) || + ADD_OVERFLOW (newbytes, extra_items * itemsize, &newbytes)) {

+ errno = ENOMEM; + return -1; + } + } + +#ifdef HAVE_POSIX_MEMALIGN + if ((r = posix_memalign (&newptr, pagesize, newbytes)) != 0) { + errno = r; + return -1; + } +#elif HAVE_VALLOC + newptr = valloc (newbytes); + if (newptr == NULL) + return -1; +#else +#error "this platform does not have posix_memalign or valloc" +#endif + + /* NB: reserve always makes the buffer larger so we don't have to + * deal with the case of a shrinking buffer here. Also reserve + * (like the underlying realloc) does not zero the reserved + * elements. So we're just copying over the old elements here. + */ + memcpy (newptr, v->ptr, v->len * itemsize); + free (v->ptr); + v->ptr = newptr; + v->cap = newcap; + return 0; +}