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qemu: do crash safe creation of NVRAM file

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If we crash part way through writing the NVRAM file we end up with an
unusable NVRAM on file. To avoid this we need to write to a temporary
file and fsync(2) at the end, then rename to the real NVRAM file path.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2022-02-03 16:15:51 +00:00
parent 2df9031a0e
commit 5e3498744e
1 changed files with 20 additions and 4 deletions
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24
src/qemu/qemu_process.c
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@ -4433,6 +4433,7 @@ qemuPrepareNVRAM(virQEMUDriver *driver,
bool created = false;
const char *master_nvram_path;
ssize_t r;
g_autofree char *tmp_dst_path = NULL;
if (!loader || !loader->nvram || virFileExists(loader->nvram))
return 0;
@ -4463,14 +4464,15 @@ qemuPrepareNVRAM(virQEMUDriver *driver,
goto cleanup;
}
if ((dstFD = virFileOpenAs(loader->nvram,
tmp_dst_path = g_strdup_printf("%s.tmp", loader->nvram);
if ((dstFD = virFileOpenAs(tmp_dst_path,
O_WRONLY | O_CREAT | O_EXCL,
S_IRUSR | S_IWUSR,
cfg->user, cfg->group,
VIR_FILE_OPEN_FORCE_OWNER)) < 0) {
virReportSystemError(-dstFD,
_("Failed to create file '%s'"),
loader->nvram);
tmp_dst_path);
goto cleanup;
}
@ -4489,7 +4491,7 @@ qemuPrepareNVRAM(virQEMUDriver *driver,
if (safewrite(dstFD, buf, r) < 0) {
virReportSystemError(errno,
_("Unable to write to file '%s'"),
loader->nvram);
tmp_dst_path);
goto cleanup;
}
} while (r);
@ -4500,9 +4502,23 @@ qemuPrepareNVRAM(virQEMUDriver *driver,
master_nvram_path);
goto cleanup;
}
if (g_fsync(dstFD) < 0) {
virReportSystemError(errno, _("cannot sync file '%s'"),
tmp_dst_path);
goto cleanup;
}
if (VIR_CLOSE(dstFD) < 0) {
virReportSystemError(errno,
_("Unable to close file '%s'"),
tmp_dst_path);
goto cleanup;
}
if (rename(tmp_dst_path, loader->nvram) < 0) {
virReportSystemError(errno,
_("Unable to replace '%s'"),
loader->nvram);
goto cleanup;
}
@ -4513,7 +4529,7 @@ qemuPrepareNVRAM(virQEMUDriver *driver,
* copy the file content. Roll back. */
if (ret < 0) {
if (created)
unlink(loader->nvram);
unlink(tmp_dst_path);
}
VIR_FORCE_CLOSE(srcFD);