This is similar to one of previous patches. When receiving stream (on virStorageVolUpload() and subsequent virStreamSparseSendAll()) we may receive a hole. If the volume we are saving the incoming data into is a regular file we just lseek() and ftruncate() to create the hole. But this won't work if the file is a block device. If that is the case we must write zeroes so that any subsequent reader reads nothing just zeroes (just like they would from a hole in a regular file). Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1852528 Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> Reviewed-by: Peter Krempa <pkrempa@xxxxxxxxxx> --- src/util/virfdstream.c | 59 +++++++++++++++++++++++++++++++----------- 1 file changed, 44 insertions(+), 15 deletions(-) diff --git a/src/util/virfdstream.c b/src/util/virfdstream.c index 39514ef555..1a7b671179 100644 --- a/src/util/virfdstream.c +++ b/src/util/virfdstream.c @@ -512,6 +512,7 @@ virFDStreamThreadDoRead(virFDStreamDataPtr fdst, static ssize_t virFDStreamThreadDoWrite(virFDStreamDataPtr fdst, bool sparse, + bool isBlock, const int fdin, const int fdout, const char *fdinname, @@ -519,7 +520,6 @@ virFDStreamThreadDoWrite(virFDStreamDataPtr fdst, { ssize_t got = 0; virFDStreamMsgPtr msg = fdst->msg; - off_t off; bool pop = false; switch (msg->type) { @@ -547,19 +547,48 @@ virFDStreamThreadDoWrite(virFDStreamDataPtr fdst, } got = msg->stream.hole.len; - off = lseek(fdout, got, SEEK_CUR); - if (off == (off_t) -1) { - virReportSystemError(errno, - _("unable to seek in %s"), - fdoutname); - return -1; - } - - if (ftruncate(fdout, off) < 0) { - virReportSystemError(errno, - _("unable to truncate %s"), - fdoutname); - return -1; + if (isBlock) { + g_autofree char * buf = NULL; + const size_t buflen = 1 * 1024 * 1024; /* 1MiB */ + size_t toWrite = got; + + /* While for files it's enough to lseek() and ftruncate() to create + * a hole which would emulate zeroes on read(), for block devices + * we have to write zeroes to read() zeroes. And we have to write + * @got bytes of zeroes. Do that in smaller chunks though.*/ + + buf = g_new0(char, buflen); + + while (toWrite) { + size_t count = MIN(toWrite, buflen); + ssize_t r; + + if ((r = safewrite(fdout, buf, count)) < 0) { + virReportSystemError(errno, + _("Unable to write %s"), + fdoutname); + return -1; + } + + toWrite -= r; + } + } else { + off_t off; + + off = lseek(fdout, got, SEEK_CUR); + if (off == (off_t) -1) { + virReportSystemError(errno, + _("unable to seek in %s"), + fdoutname); + return -1; + } + + if (ftruncate(fdout, off) < 0) { + virReportSystemError(errno, + _("unable to truncate %s"), + fdoutname); + return -1; + } } pop = true; @@ -625,7 +654,7 @@ virFDStreamThread(void *opaque) length, total, &dataLen, buflen); else - got = virFDStreamThreadDoWrite(fdst, sparse, + got = virFDStreamThreadDoWrite(fdst, sparse, isBlock, fdin, fdout, fdinname, fdoutname); -- 2.26.2
