[PATCH] Clean up expand_fdtable() and expand_files(), take 2.

[Vadim Lobanov]

Hi,

This patch performs a code cleanup against the expand_fdtable() and 
expand_files() functions inside fs/file.c It aims to make the flow of code 
within these functions simpler and easier to understand, via added comments 
and modest refactoring. The patch was generated against 2.6.18-rc5-mm1, and 
was successfully run live. Andrew, please apply.

Changes for take 2:
As per Randy's suggestion, the function header comments were expanded to be 
more explanatory and explicit.

Signed-off-by: Vadim Lobanov <vlobanov@xxxxxxxxxxxxx>

diff -Npru linux-a/fs/file.c linux-b/fs/file.c
--- linux-a/fs/file.c	2006-09-01 20:34:12.000000000 -0700
+++ linux-b/fs/file.c	2006-09-05 12:16:52.000000000 -0700
@@ -288,71 +288,65 @@ out:
 }
 
 /*
- * Expands the file descriptor table - it will allocate a new fdtable and
- * both fd array and fdset. It is expected to be called with the
- * files_lock held.
+ * Expand the file descriptor table.
+ * This function will allocate a new fdtable and both fd array and fdset, of
+ * the given size.
+ * Return <0 error code on error; 1 on successful completion.
+ * The files->file_lock should be held on entry, and will be held on exit.
  */
 static int expand_fdtable(struct files_struct *files, int nr)
 	__releases(files->file_lock)
 	__acquires(files->file_lock)
 {
-	int error = 0;
-	struct fdtable *fdt;
-	struct fdtable *nfdt = NULL;
+	struct fdtable *new_fdt, *cur_fdt;
 
 	spin_unlock(&files->file_lock);
-	nfdt = alloc_fdtable(nr);
-	if (!nfdt) {
-		error = -ENOMEM;
-		spin_lock(&files->file_lock);
-		goto out;
-	}
-
+	new_fdt = alloc_fdtable(nr);
 	spin_lock(&files->file_lock);
-	fdt = files_fdtable(files);
+	if (!new_fdt)
+		return -ENOMEM;
 	/*
-	 * Check again since another task may have expanded the
-	 * fd table while we dropped the lock
+	 * Check again since another task may have expanded the fd table while
+	 * we dropped the lock
 	 */
-	if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
-		copy_fdtable(nfdt, fdt);
+	cur_fdt = files_fdtable(files);
+	if (nr >= cur_fdt->max_fds || nr >= cur_fdt->max_fdset) {
+		/* Continue as planned */
+		copy_fdtable(new_fdt, cur_fdt);
+		rcu_assign_pointer(files->fdt, new_fdt);
+		free_fdtable(cur_fdt);
 	} else {
-		/* Somebody expanded while we dropped file_lock */
+		/* Somebody else expanded, so undo our attempt */
 		spin_unlock(&files->file_lock);
-		__free_fdtable(nfdt);
+		__free_fdtable(new_fdt);
 		spin_lock(&files->file_lock);
-		goto out;
 	}
-	rcu_assign_pointer(files->fdt, nfdt);
-	free_fdtable(fdt);
-out:
-	return error;
+	return 1;
 }
 
 /*
  * Expand files.
- * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
- * Should be called with the files->file_lock spinlock held for write.
+ * This function will expand the file structures, if the requested size 
exceeds
+ * the current capacity and there is room for expansion.
+ * Return <0 error code on error; 0 when nothing done; 1 when files were
+ * expanded and execution may have blocked.
+ * The files->file_lock should be held on entry, and will be held on exit.
  */
 int expand_files(struct files_struct *files, int nr)
 {
-	int err, expand = 0;
 	struct fdtable *fdt;
 
 	fdt = files_fdtable(files);
-	if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
-		if (fdt->max_fdset >= NR_OPEN ||
-			fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
-			err = -EMFILE;
-			goto out;
-		}
-		expand = 1;
-		if ((err = expand_fdtable(files, nr)))
-			goto out;
-	}
-	err = expand;
-out:
-	return err;
+	/* Do we need to expand? */
+	if (nr < fdt->max_fdset && nr < fdt->max_fds)
+		return 0;
+	/* Can we expand? */
+	if (fdt->max_fdset >= NR_OPEN || fdt->max_fds >= NR_OPEN ||
+	    nr >= NR_OPEN)
+		return -EMFILE;
+
+	/* All good, so we try */
+	return expand_fdtable(files, nr);
 }
 
 static void __devinit fdtable_defer_list_init(int cpu)
-
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