libc: Add faster scandir function(scandir_sane).

This function is significantly faster due to not requiring memory
allocations for each directory entry. Now they are instead just
allocated as a large chunk. This function is not compatible with scandir
since the cleanup of both function will be different.

With this a new function scandir_sane_free has also been added.

Besides having a function(like scandir) that forces the programmer to
implement their own cleanup procedure that is anymore complicated than a
simple free() call is absurd.

1 files changed, 60 insertions, 0 deletions

diff --git a/userland/libc/dirent/scandir.c b/userland/libc/dirent/scandir.c
index 564cbc8..3ac040a 100644
--- a/userland/libc/dirent/scandir.c
+++ b/userland/libc/dirent/scandir.c
@@ -1,12 +1,72 @@
 #include <dirent.h>
+#include <fcntl.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 int nop_compar(const struct dirent **d1, const struct dirent **d2) {
   *d2 = *d1;
   return 0;
 }
 
+// Differs from scandir in the sense that the namelist has its own way
+// of allocating its entries(in this case it allocates it as a large
+// chunk). As a result the usual free() operation can not be ran on
+// the elements.
+//
+// Instead scandir_sane_free() should be used to deallocate the
+// namelist.
+int scandir_sane(const char *dir, struct dirent ***namelist,
+                 int (*sel)(const struct dirent *),
+                 int (*compar)(const struct dirent **,
+                               const struct dirent **)) {
+  if (!compar) {
+    compar = nop_compar;
+  }
+
+  int fd = open(dir, O_RDONLY);
+  if (-1 == fd) {
+    // TODO: Figure out what to set errno to
+    return -1;
+  }
+
+  size_t capacity = 128;
+  size_t num_entries;
+  struct dirent *chunk = NULL;
+  for (;;) {
+    chunk = realloc(chunk, sizeof(struct dirent) * capacity);
+    int rc = pread(fd, chunk, sizeof(struct dirent) * capacity, 0);
+    if (-1 == rc) {
+      free(chunk);
+      // TODO: Figure out what to set errno to
+      return -1;
+    }
+    if (sizeof(struct dirent) * capacity == (size_t)rc) {
+      // The directory **may** contain more entries.
+      // Redo
+      capacity *= 2;
+      continue;
+    }
+    num_entries = rc / (sizeof(struct dirent));
+    break;
+  }
+
+  *namelist = allocarray(num_entries, sizeof(struct dirent *));
+
+  for (size_t i = 0; i < num_entries; i++) {
+    (*namelist)[i] = &chunk[i];
+  }
+
+  close(fd);
+  return num_entries;
+}
+
+void scandir_sane_free(struct dirent **namelist) {
+  free(namelist[0]); // First pointer is the start of the chunk in the
+                     // current implementation
+  free(namelist);
+}
+
 int scandir(const char *dir, struct dirent ***namelist,
             int (*sel)(const struct dirent *),
             int (*compar)(const struct dirent **, const struct dirent **)) {