[Libguestfs] [libguestfs PATCH 2/2] guestfs_readdir(): minimize the number of send_file_write() calls
In guestfs_readdir(), the daemon currently sends each XDR-encoded
"guestfs_int_dirent" to the library with a separate send_file_write()
call.
Determine the largest encoded size (from the longest filename that a
"guestfs_int_dirent" could carry, from readdir()'s "struct
dirent"), and
batch up the XDR encodings until the next encoding might not fit in
GUESTFS_MAX_CHUNK_SIZE. Call send_file_write() only then.
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1674392
Signed-off-by: Laszlo Ersek <lersek(a)redhat.com>
---
daemon/readdir.c | 38 ++++++++++++++++----
1 file changed, 32 insertions(+), 6 deletions(-)
diff --git a/daemon/readdir.c b/daemon/readdir.c
index 9ab0b0aec955..3084ba939c10 100644
--- a/daemon/readdir.c
+++ b/daemon/readdir.c
@@ -35,6 +35,9 @@ do_internal_readdir (const char *dir)
DIR *dirstream;
void *xdr_buf;
XDR xdr;
+ struct dirent fill;
+ guestfs_int_dirent v;
+ unsigned max_encoded;
/* Prepare to fail. */
ret = -1;
@@ -55,6 +58,20 @@ do_internal_readdir (const char *dir)
}
xdrmem_create (&xdr, xdr_buf, GUESTFS_MAX_CHUNK_SIZE, XDR_ENCODE);
+ /* Calculate the max number of bytes a "guestfs_int_dirent" can be encoded
to.
+ */
+ memset (fill.d_name, 'a', sizeof fill.d_name - 1);
+ fill.d_name[sizeof fill.d_name - 1] = '\0';
+ v.ino = INT64_MAX;
+ v.ftyp = '?';
+ v.name = fill.d_name;
+ if (!xdr_guestfs_int_dirent (&xdr, &v)) {
+ fprintf (stderr, "xdr_guestfs_int_dirent failed\n");
+ goto release_xdr;
+ }
+ max_encoded = xdr_getpos (&xdr);
+ xdr_setpos (&xdr, 0);
+
/* Send an "OK" reply, before starting the file transfer. */
reply (NULL, NULL);
@@ -63,7 +80,6 @@ do_internal_readdir (const char *dir)
*/
for (;;) {
struct dirent *d;
- guestfs_int_dirent v;
errno = 0;
d = readdir (dirstream);
@@ -94,22 +110,32 @@ do_internal_readdir (const char *dir)
v.ftyp = 'u';
#endif
+ /* Flush "xdr_buf" if we may not have enough room for encoding
"v". */
+ if (GUESTFS_MAX_CHUNK_SIZE - xdr_getpos (&xdr) < max_encoded) {
+ if (send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
+ break;
+
+ xdr_setpos (&xdr, 0);
+ }
+
if (!xdr_guestfs_int_dirent (&xdr, &v)) {
fprintf (stderr, "xdr_guestfs_int_dirent failed\n");
break;
}
-
- if (send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
- break;
-
- xdr_setpos (&xdr, 0);
}
+ /* Flush "xdr_buf" if the loop completed successfully and "xdr_buf"
is not
+ * empty. */
+ if (ret == 0 && xdr_getpos (&xdr) > 0 &&
+ send_file_write (xdr_buf, xdr_getpos (&xdr)) != 0)
+ ret = -1;
+
/* Finish or cancel the transfer. Note that if (ret == -1) because the library
* canceled, we still need to cancel back!
*/
send_file_end (ret == -1);
+release_xdr:
xdr_destroy (&xdr);
free (xdr_buf);
--
2.19.1.3.g30247aa5d201