src/lib/file-set-size.c

/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#ifdef HAVE_POSIX_FALLOCATE
#  define _XOPEN_SOURCE 600 /* Required by glibc, breaks Solaris 9 */
#endif
#define _GNU_SOURCE /* for fallocate() */
#include "lib.h"
#include "file-set-size.h"

#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#if defined(HAVE_LINUX_FALLOC_H) && !defined(FALLOC_FL_KEEP_SIZE)
/* Legacy Linux does not have the FALLOC_FL_* flags under fcntl.h */
#  include <linux/falloc.h>
#endif

int file_set_size(int fd, off_t size)
{
#ifdef HAVE_POSIX_FALLOCATE
    static bool posix_fallocate_supported = TRUE;
#endif
    char block[IO_BLOCK_SIZE];
    off_t offset;
    ssize_t ret;
    struct stat st;

    i_assert(size >= 0);

    if (fstat(fd, &st) < 0) {
        i_error("fstat() failed: %m");
        return -1;
    }

    if (size < st.st_size) {
        if (ftruncate(fd, size) < 0) {
            i_error("ftruncate() failed: %m");
            return -1;
        }
        return 0;
    }
    if (size == st.st_size)
        return 0;

#ifdef HAVE_POSIX_FALLOCATE
    if (posix_fallocate_supported) {
        int err;

        err = posix_fallocate(fd, st.st_size, size - st.st_size);
        if (err == 0)
            return 0;

        if (err != EINVAL /* Solaris */ &&
            err != EOPNOTSUPP /* AOX */) {
            if (!ENOSPACE(err))
                i_error("posix_fallocate() failed: %m");
            return -1;
        }
        /* Not supported by kernel, fallback to writing. */
        posix_fallocate_supported = FALSE;
    }
#endif
    /* start growing the file */
    offset = st.st_size;
    memset(block, 0, I_MIN((ssize_t)sizeof(block), size - offset));

    while (offset < size) {
        ret = pwrite(fd, block,
                 I_MIN((ssize_t)sizeof(block), size - offset),
                 offset);
        if (ret < 0) {
            if (!ENOSPACE(errno))
                i_error("pwrite() failed: %m");
            return -1;
        }
        offset += ret;
    }
    return 0;
}

int file_preallocate(int fd ATTR_UNUSED, off_t size ATTR_UNUSED)
{
#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_KEEP_SIZE)
    /* Linux */
    if (fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, size) < 0)
        return errno == ENOSYS ? 0 : -1;
    return 1;
#elif defined (F_PREALLOCATE)
    /* OSX */
    fstore_t fs;

    i_zero(&fs);
    fs.fst_flags = F_ALLOCATECONTIG;
    fs.fst_posmode = F_PEOFPOSMODE;
    fs.fst_offset = 0;
    fs.fst_length = size;
    fs.fst_bytesalloc = 0;
    if (fcntl(fd, F_PREALLOCATE, &fs) < 0)
        return -1;
    return fs.fst_bytesalloc > 0 ? 1 : 0;
#else
    return 0;
#endif
}