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virfdstream: Emulate skip for block devices

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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@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
This commit is contained in:
Michal Privoznik 2020-07-01 21:39:40 +02:00
parent 9e0ba037cd
commit fd6b531cb2
1 changed files with 43 additions and 14 deletions
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57
src/util/virfdstream.c
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@ -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 (isBlock) {
g_autofree char * buf = NULL;
const size_t buflen = 1 * 1024 * 1024; /* 1MiB */
size_t toWrite = got;
if (ftruncate(fdout, off) < 0) {
virReportSystemError(errno,
_("unable to truncate %s"),
fdoutname);
return -1;
/* 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);