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kernel: relay: remove relay_file_splice_read dead code, doesn't work

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Documentation/filesystems/relay.rst says to use
	return debugfs_create_file(filename, mode, parent, buf,
	                           &relay_file_operations);
and this is the only way relay_file_operations is used.

Thus: debugfs_create_file(&relay_file_operations)
   -> __debugfs_create_file(&debugfs_full_proxy_file_operations,
                            &relay_file_operations)
   -> dentry{inode: {i_fop: &debugfs_full_proxy_file_operations},
             d_fsdata: &relay_file_operations
                       | DEBUGFS_FSDATA_IS_REAL_FOPS_BIT}

debugfs_full_proxy_file_operations.open is full_proxy_open, which extracts
the &relay_file_operations from the dentry, and allocates via
__full_proxy_fops_init() new fops, with trivial wrappers around release,
llseek, read, write, poll, and unlocked_ioctl, then replaces the fops on
the opened file therewith.

Naturally, all thusly-created debugfs files have .splice_read = NULL. 
This was introduced in commit 49d200deaa ("debugfs: prevent access to
removed files' private data") from 2016-03-22.

AFAICT, relay_file_operations is the only struct file_operations used for
debugfs which defines a .splice_read callback.  Hooking it up with

>	diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>	index 5063434be0fc..952fcf5b2afa 100644
>	--- a/fs/debugfs/file.c
>	+++ b/fs/debugfs/file.c
>	@@ -328,6 +328,11 @@ FULL_PROXY_FUNC(write, ssize_t, filp,
>	 			loff_t *ppos),
>	 		ARGS(filp, buf, size, ppos));
>
>	+FULL_PROXY_FUNC(splice_read, long, in,
>	+		PROTO(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe,
>	+			size_t len, unsigned int flags),
>	+		ARGS(in, ppos, pipe, len, flags));
>	+
>	 FULL_PROXY_FUNC(unlocked_ioctl, long, filp,
>	 		PROTO(struct file *filp, unsigned int cmd, unsigned long arg),
>	 		ARGS(filp, cmd, arg));
>	@@ -382,6 +387,8 @@ static void __full_proxy_fops_init(struct file_operations *proxy_fops,
>	 		proxy_fops->write = full_proxy_write;
>	 	if (real_fops->poll)
>	 		proxy_fops->poll = full_proxy_poll;
>	+	if (real_fops->splice_read)
>	+		proxy_fops->splice_read = full_proxy_splice_read;
>	 	if (real_fops->unlocked_ioctl)
>	 		proxy_fops->unlocked_ioctl = full_proxy_unlocked_ioctl;
>	 }

shows it just doesn't work, and splicing always instantly returns empty
(subsequent reads actually return the contents).

No-one noticed it became dead code in 2016, who knows if it worked back
then. Clearly no-one cares; just delete it.

Link: https://lkml.kernel.org/r/dtexwpw6zcdx7dkx3xj5gyjp5syxmyretdcbcdtvrnukd4vvuh@tarta.nabijaczleweli.xyz
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Li kunyu <kunyu@nfschina.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zhang Zhengming <zhang.zhengming@h3c.com>
Cc: Zhao Lei <zhao_lei1@hoperun.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ahelenia Ziemiańska 2023-12-19 23:24:14 +01:00 committed by Andrew Morton
parent 50bc98323c
commit d391615618
1 changed files with 0 additions and 162 deletions
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162
kernel/relay.c
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@ -1073,167 +1073,6 @@ static ssize_t relay_file_read(struct file *filp,
return written;
}
static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
{
rbuf->bytes_consumed += bytes_consumed;
if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
}
}
static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct rchan_buf *rbuf;
rbuf = (struct rchan_buf *)page_private(buf->page);
relay_consume_bytes(rbuf, buf->private);
}
static const struct pipe_buf_operations relay_pipe_buf_ops = {
.release = relay_pipe_buf_release,
.try_steal = generic_pipe_buf_try_steal,
.get = generic_pipe_buf_get,
};
static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
{
}
/*
* subbuf_splice_actor - splice up to one subbuf's worth of data
*/
static ssize_t subbuf_splice_actor(struct file *in,
loff_t *ppos,
struct pipe_inode_info *pipe,
size_t len,
unsigned int flags,
int *nonpad_ret)
{
unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
struct rchan_buf *rbuf = in->private_data;
unsigned int subbuf_size = rbuf->chan->subbuf_size;
uint64_t pos = (uint64_t) *ppos;
uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
size_t read_start = (size_t) do_div(pos, alloc_size);
size_t read_subbuf = read_start / subbuf_size;
size_t padding = rbuf->padding[read_subbuf];
size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
struct page *pages[PIPE_DEF_BUFFERS];
struct partial_page partial[PIPE_DEF_BUFFERS];
struct splice_pipe_desc spd = {
.pages = pages,
.nr_pages = 0,
.nr_pages_max = PIPE_DEF_BUFFERS,
.partial = partial,
.ops = &relay_pipe_buf_ops,
.spd_release = relay_page_release,
};
ssize_t ret;
if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
return 0;
if (splice_grow_spd(pipe, &spd))
return -ENOMEM;
/*
* Adjust read len, if longer than what is available
*/
if (len > (subbuf_size - read_start % subbuf_size))
len = subbuf_size - read_start % subbuf_size;
subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
pidx = (read_start / PAGE_SIZE) % subbuf_pages;
poff = read_start & ~PAGE_MASK;
nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
unsigned int this_len, this_end, private;
unsigned int cur_pos = read_start + total_len;
if (!len)
break;
this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
private = this_len;
spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
spd.partial[spd.nr_pages].offset = poff;
this_end = cur_pos + this_len;
if (this_end >= nonpad_end) {
this_len = nonpad_end - cur_pos;
private = this_len + padding;
}
spd.partial[spd.nr_pages].len = this_len;
spd.partial[spd.nr_pages].private = private;
len -= this_len;
total_len += this_len;
poff = 0;
pidx = (pidx + 1) % subbuf_pages;
if (this_end >= nonpad_end) {
spd.nr_pages++;
break;
}
}
ret = 0;
if (!spd.nr_pages)
goto out;
ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
if (ret < 0 || ret < total_len)
goto out;
if (read_start + ret == nonpad_end)
ret += padding;
out:
splice_shrink_spd(&spd);
return ret;
}
static ssize_t relay_file_splice_read(struct file *in,
loff_t *ppos,
struct pipe_inode_info *pipe,
size_t len,
unsigned int flags)
{
ssize_t spliced;
int ret;
int nonpad_ret = 0;
ret = 0;
spliced = 0;
while (len && !spliced) {
ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
if (ret < 0)
break;
else if (!ret) {
if (flags & SPLICE_F_NONBLOCK)
ret = -EAGAIN;
break;
}
*ppos += ret;
if (ret > len)
len = 0;
else
len -= ret;
spliced += nonpad_ret;
nonpad_ret = 0;
}
if (spliced)
return spliced;
return ret;
}
const struct file_operations relay_file_operations = {
.open = relay_file_open,
@ -1242,6 +1081,5 @@ const struct file_operations relay_file_operations = {
.read = relay_file_read,
.llseek = no_llseek,
.release = relay_file_release,
.splice_read = relay_file_splice_read,
};
EXPORT_SYMBOL_GPL(relay_file_operations);