diff options
author | Kevin Wolf <kwolf@redhat.com> | 2011-08-26 15:27:13 +0200 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2011-08-29 14:42:39 +0200 |
commit | a22f123ca3d3c09a77af4341ed1fbcc175b54f1d (patch) | |
tree | b9992c37d4a4645e6282375c669ae1e771206a1c /qemu-img.c | |
parent | c488c7f649106d09df76f697adccbe6e72520b26 (diff) | |
download | hqemu-a22f123ca3d3c09a77af4341ed1fbcc175b54f1d.zip hqemu-a22f123ca3d3c09a77af4341ed1fbcc175b54f1d.tar.gz |
qemu-img: Require larger zero areas for sparse handling
By default, require 4k of consecutive zero bytes for qemu-img to make the
output file sparse by not issuing a write request for the zeroed parts. Add an
-S option to allow users to tune this setting.
This helps to avoid situations where a lot of zero sectors and data sectors are
mixed and qemu-img tended to issue many tiny 512 byte writes.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-img.c')
-rw-r--r-- | qemu-img.c | 61 |
1 files changed, 59 insertions, 2 deletions
@@ -82,6 +82,8 @@ static void help(void) " rebasing in this case (useful for renaming the backing file)\n" " '-h' with or without a command shows this help and lists the supported formats\n" " '-p' show progress of command (only certain commands)\n" + " '-S' indicates the consecutive number of bytes that must contain only zeros\n" + " for qemu-img to create a sparse image during conversion\n" "\n" "Parameters to snapshot subcommand:\n" " 'snapshot' is the name of the snapshot to create, apply or delete\n" @@ -571,6 +573,48 @@ static int is_allocated_sectors(const uint8_t *buf, int n, int *pnum) } /* + * Like is_allocated_sectors, but if the buffer starts with a used sector, + * up to 'min' consecutive sectors containing zeros are ignored. This avoids + * breaking up write requests for only small sparse areas. + */ +static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum, + int min) +{ + int ret; + int num_checked, num_used; + + if (n < min) { + min = n; + } + + ret = is_allocated_sectors(buf, n, pnum); + if (!ret) { + return ret; + } + + num_used = *pnum; + buf += BDRV_SECTOR_SIZE * *pnum; + n -= *pnum; + num_checked = num_used; + + while (n > 0) { + ret = is_allocated_sectors(buf, n, pnum); + + buf += BDRV_SECTOR_SIZE * *pnum; + n -= *pnum; + num_checked += *pnum; + if (ret) { + num_used = num_checked; + } else if (*pnum >= min) { + break; + } + } + + *pnum = num_used; + return 1; +} + +/* * Compares two buffers sector by sector. Returns 0 if the first sector of both * buffers matches, non-zero otherwise. * @@ -620,6 +664,7 @@ static int img_convert(int argc, char **argv) char *options = NULL; const char *snapshot_name = NULL; float local_progress; + int min_sparse = 8; /* Need at least 4k of zeros for sparse detection */ fmt = NULL; out_fmt = "raw"; @@ -627,7 +672,7 @@ static int img_convert(int argc, char **argv) out_baseimg = NULL; compress = 0; for(;;) { - c = getopt(argc, argv, "f:O:B:s:hce6o:pt:"); + c = getopt(argc, argv, "f:O:B:s:hce6o:pS:t:"); if (c == -1) { break; } @@ -662,6 +707,18 @@ static int img_convert(int argc, char **argv) case 's': snapshot_name = optarg; break; + case 'S': + { + int64_t sval; + sval = strtosz_suffix(optarg, NULL, STRTOSZ_DEFSUFFIX_B); + if (sval < 0) { + error_report("Invalid minimum zero buffer size for sparse output specified"); + return 1; + } + + min_sparse = sval / BDRV_SECTOR_SIZE; + break; + } case 'p': progress = 1; break; @@ -970,7 +1027,7 @@ static int img_convert(int argc, char **argv) sectors that are entirely 0, since whatever data was already there is garbage, not 0s. */ if (!has_zero_init || out_baseimg || - is_allocated_sectors(buf1, n, &n1)) { + is_allocated_sectors_min(buf1, n, &n1, min_sparse)) { ret = bdrv_write(out_bs, sector_num, buf1, n1); if (ret < 0) { error_report("error while writing sector %" PRId64 |