xenstore: support XS_DIRECTORY_PART in libxenstore

This will enable all users of libxenstore to handle xenstore nodes
with a huge amount of children.

In order to not depend completely on the XS_DIRECTORY_PART
functionality use it only in case of E2BIG returned by XS_DIRECTORY.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index d1e01babb6a5e03ad2c6d2b19a4b1de789bdfec5..40e32750dad3c6d748268b78c24dc6e0667c01b4 100644 (file)
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -558,15 +558,10 @@ static bool xs_bool(char *reply)
        return true;
 }
 
-char **xs_directory(struct xs_handle *h, xs_transaction_t t,
-                   const char *path, unsigned int *num)
+static char **xs_directory_common(char *strings, unsigned int len,
+                                 unsigned int *num)
 {
-       char *strings, *p, **ret;
-       unsigned int len;
-
-       strings = xs_single(h, t, XS_DIRECTORY, path, &len);
-       if (!strings)
-               return NULL;
+       char *p, **ret;
 
        /* Count the strings. */
        *num = xs_count_strings(strings, len);
@@ -586,6 +581,75 @@ char **xs_directory(struct xs_handle *h, xs_transaction_t t,
        return ret;
 }
 
+static char **xs_directory_part(struct xs_handle *h, xs_transaction_t t,
+                               const char *path, unsigned int *num)
+{
+       unsigned int off, result_len;
+       char gen[24], offstr[8];
+       struct iovec iovec[2];
+       char *result = NULL, *strings = NULL;
+
+       gen[0] = 0;
+       iovec[0].iov_base = (void *)path;
+       iovec[0].iov_len = strlen(path) + 1;
+
+       for (off = 0;;) {
+               snprintf(offstr, sizeof(offstr), "%u", off);
+               iovec[1].iov_base = (void *)offstr;
+               iovec[1].iov_len = strlen(offstr) + 1;
+               result = xs_talkv(h, t, XS_DIRECTORY_PART, iovec, 2,
+                                 &result_len);
+
+               /* If XS_DIRECTORY_PART isn't supported return E2BIG. */
+               if (!result) {
+                       if (errno == ENOSYS)
+                               errno = E2BIG;
+                       return NULL;
+               }
+
+               if (off) {
+                       if (strcmp(gen, result)) {
+                               free(result);
+                               free(strings);
+                               strings = NULL;
+                               off = 0;
+                               continue;
+                       }
+               } else
+                       strncpy(gen, result, sizeof(gen));
+
+               result_len -= strlen(result) + 1;
+               strings = realloc(strings, off + result_len);
+               memcpy(strings + off, result + strlen(result) + 1, result_len);
+               free(result);
+               off += result_len;
+
+               if (off <= 1 || strings[off - 2] == 0)
+                       break;
+       }
+
+       if (off > 1)
+               off--;
+
+       return xs_directory_common(strings, off, num);
+}
+
+char **xs_directory(struct xs_handle *h, xs_transaction_t t,
+                   const char *path, unsigned int *num)
+{
+       char *strings;
+       unsigned int len;
+
+       strings = xs_single(h, t, XS_DIRECTORY, path, &len);
+       if (!strings) {
+               if (errno != E2BIG)
+                       return NULL;
+               return xs_directory_part(h, t, path, num);
+       }
+
+       return xs_directory_common(strings, len, num);
+}
+
 /* Get the value of a single file, nul terminated.
  * Returns a malloced value: call free() on it after use.
  * len indicates length in bytes, not including the nul.