[Libguestfs] [PATCH 2/2] Discard unwritten ranges

--- pxzcat.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/pxzcat.c b/pxzcat.c index 9bcdc36..55ccfc0 100644 --- a/pxzcat.c +++ b/pxzcat.c @@ -44,10 +44,11 @@ #include <sys/types.h> #include <error.h> #include <errno.h> #include <getopt.h> #include <pthread.h> +#include <linux/falloc.h> #include <lzma.h> #define DEBUG 0 @@ -145,10 +146,11 @@ usage (int exitcode) static void xzfile_uncompress (const char *filename, const char *outputfile, unsigned nr_threads) { int fd, ofd; + off_t hole_start, data_start; uint64_t size; lzma_index *idx; /* Open the file. */ fd = open (filename, O_RDONLY); @@ -176,10 +178,29 @@ xzfile_uncompress (const char *filename, const char *outputfile, posix_fadvise (fd, 0, 0, POSIX_FADV_RANDOM|POSIX_FADV_DONTNEED); /* Iterate over blocks. */ iter_blocks (idx, nr_threads, filename, fd, outputfile, ofd); + /* discard ranges that were allocated but not written */ + data_start = 0; + while (data_start < size) { + hole_start = lseek (ofd, data_start, SEEK_HOLE); + if (hole_start == (off_t) -1) + error (EXIT_FAILURE, errno, "lseek: %s", outputfile); + if (hole_start == size) + break; + data_start = lseek (ofd, hole_start, SEEK_DATA); + if (data_start == (off_t) -1) { + if (errno == ENXIO) + data_start = size; + else + error (EXIT_FAILURE, errno, "lseek: %s", outputfile); + } + if (fallocate (ofd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, hole_start, data_start - hole_start) == -1) + error (EXIT_FAILURE, errno, "fallocate: %s", outputfile); + } + close (fd); } static int check_header_magic (int fd) -- 1.8.4.1.563.g8e6fc32