eventfs: Shortcut eventfs_iterate() by skipping entries already read

As the ei->entries array is fixed for the duration of the eventfs_inode,
it can be used to skip over already read entries in eventfs_iterate().

That is, if ctx->pos is greater than zero, there's no reason in doing the
loop across the ei->entries array for the entries less than ctx->pos.
Instead, start the lookup of the entries at the current ctx->pos.

Link: https://lore.kernel.org/all/CAHk-=wiKwDUDv3+jCsv-uacDcHDVTYsXtBR9=6sGM5mqX+DhOg@mail.gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/20240104220048.494956957@goodmis.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index a1934e0eea3b7df83a22fa8ca7fba07d570bac6b..fdff53d5a1f87f063448d2e6bd2185ad18e1a3c2 100644 (file)
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -746,21 +746,15 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
        if (!ei || !ei_dentry)
                goto out;
 
-       ret = 0;
-
        /*
         * Need to create the dentries and inodes to have a consistent
         * inode number.
         */
-       for (i = 0; i < ei->nr_entries; i++) {
-               void *cdata = ei->data;
-
-               if (c > 0) {
-                       c--;
-                       continue;
-               }
+       ret = 0;
 
-               ctx->pos++;
+       /* Start at 'c' to jump over already read entries */
+       for (i = c; i < ei->nr_entries; i++, ctx->pos++) {
+               void *cdata = ei->data;
 
                entry = &ei->entries[i];
                name = entry->name;
@@ -769,7 +763,7 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
                /* If ei->is_freed then just bail here, nothing more to do */
                if (ei->is_freed) {
                        mutex_unlock(&eventfs_mutex);
-                       goto out_dec;
+                       goto out;
                }
                r = entry->callback(name, &mode, &cdata, &fops);
                mutex_unlock(&eventfs_mutex);
@@ -778,14 +772,17 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
 
                dentry = create_file_dentry(ei, i, ei_dentry, name, mode, cdata, fops);
                if (!dentry)
-                       goto out_dec;
+                       goto out;
                ino = dentry->d_inode->i_ino;
                dput(dentry);
 
                if (!dir_emit(ctx, name, strlen(name), ino, DT_REG))
-                       goto out_dec;
+                       goto out;
        }
 
+       /* Subtract the skipped entries above */
+       c -= min((unsigned int)c, (unsigned int)ei->nr_entries);
+
        list_for_each_entry_srcu(ei_child, &ei->children, list,
                                 srcu_read_lock_held(&eventfs_srcu)) {