Re: [libvirt] [PATCH] Fix performance problem of virStorageVolCreateXMLFrom()

> @@ -119,8 +126,10 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol, > int amtread = -1; > int ret = 0; > unsigned long long remain; > - size_t rbytes = 1024 * 1024; /* For Read */ > - char zerobuf[512]; > + size_t rbytes = READ_BLOCK_SIZE_DEFAULT; > + size_t wbytes = WRITE_BLOCK_SIZE_DEFAULT; > + int interval; > + char zerobuf[WRITE_BLOCK_SIZE_DEFAULT]; Here there is a fixed size buffer which will be written... > char *buf = NULL; > > if ((inputfd = open(inputvol->target.path, O_RDONLY)) < 0) { > @@ -131,6 +140,12 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol, > goto cleanup; > } > > +#ifdef __linux__ > + if (ioctl(fd, BLKBSZGET, &wbytes) < 0) { > + wbytes = WRITE_BLOCK_SIZE_DEFAULT; > + } > +#endif ...but the amount written is variable. So this will have an out of bounds array access if the returned 'wbytes' is greater than WRITE_BLOCK_SIZE_DEFAULT. I think you need to change 'zerobuf' to be a heap-allocated variable, instead of fixed sized stack allocated variable. eg char *zerobuf; if (VIR_ALLOC_N(zerobuf, wbytes) < 0) { virReportOOMError(); goto cleanup; } ....

> + > bzero(&zerobuf, sizeof(zerobuf)); VIR_ALLOC_N zeros, so this line could then be removed.

> > if (VIR_ALLOC_N(buf, rbytes) < 0) { > @@ -160,7 +175,7 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol, > * blocks */ > amtleft = amtread; > do { > - int interval = ((512 > amtleft) ? amtleft : 512); > + interval = ((wbytes > amtleft) ? amtleft : wbytes); > int offset = amtread - amtleft; > > if (is_dest_file && memcmp(buf+offset, zerobuf, interval) == 0) { > @@ -179,7 +194,7 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol, > goto cleanup; > > } > - } while ((amtleft -= 512) > 0); > + } while ((amtleft -= interval) > 0); > } > > if (VIR_CLOSE(inputfd) < 0) { Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|