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Subject[v6.6][PATCH 41/57] eventfs: Shortcut eventfs_iterate() by skipping entries already read
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

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>
(cherry picked from commit 1de94b52d5e8d8b32f0252f14fad1f1edc2e71f1)
---
fs/tracefs/event_inode.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index a1934e0eea3b..fdff53d5a1f8 100644
--- 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)) {

--
2.43.0


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