2006-09-05 19:27:37

by Vadim Lobanov

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

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 <[email protected]>

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)