From: Al Viro <viro@zeniv.linux.org.uk>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/6] fs: do not set no_llseek in fops
Date: Fri, 24 Jun 2022 22:48:40 +0100 [thread overview]
Message-ID: <YrYxOC5dgCKBHwVE@ZenIV> (raw)
In-Reply-To: <20220624165631.2124632-3-Jason@zx2c4.com>
On Fri, Jun 24, 2022 at 06:56:27PM +0200, Jason A. Donenfeld wrote:
> vfs_llseek already does something with this, and it makes it difficult
> to distinguish between llseek being supported and not.
How about something along the lines of
===
struct file_operations ->llseek() method gets called only in two places:
vfs_llseek() and dump_skip(). Both treat NULL and no_llseek as
equivalent.
The value of ->llseek is also examined in __full_proxy_fops_init() and
ovl_copy_up_data(). For the former we could as well treat no_llseek
as NULL; no need to do a proxy wrapper around the function that fails
with -ESPIPE without so much as looking at its arguments.
Same for the latter - there no_llseek would end up with skip_hole
set true until the first time we look at it. At that point we
call vfs_llseek(), observe that it has failed (-ESPIPE), shrug and
set skip_hole false. Might as well have done that from the very
beginning.
In other words, any place where .llseek is set to no_llseek
could just as well set it to NULL.
===
for commit message?
Next commit would remove the checks for no_llseek and have vfs_llseek()
just do
if (file->f_mode & FMODE_LSEEK) {
if (file->f_op->llseek)
return file->f_op->llseek(file, offset, whence);
}
return -ESPIPE;
and kill no_llseek() off. And once you have guaranteed that FMODE_LSEEK
is never set with NULL ->llseek, vfs_llseek() gets trimmed in obvious
way and tests in dump_skip() and ovl_copy_up_data() would become simply
file->f_mode & FMODE_LSEEK - no need to check ->f_op->llseek there
after that. At the same time dump_skip() could switch to calling
vfs_llseek() instead of direct method call...
next prev parent reply other threads:[~2022-06-24 21:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-24 16:56 [PATCH 0/6] cleanup llseek and splice Jason A. Donenfeld
2022-06-24 16:56 ` [PATCH 1/6] ksmbd: use vfs_llseek instead of dereferencing NULL Jason A. Donenfeld
2022-06-24 21:20 ` Al Viro
2022-06-25 4:10 ` Namjae Jeon
2022-06-24 16:56 ` [PATCH 2/6] fs: do not set no_llseek in fops Jason A. Donenfeld
2022-06-24 21:48 ` Al Viro [this message]
2022-06-25 10:46 ` Jason A. Donenfeld
2022-06-24 16:56 ` [PATCH 3/6] fs: clear FMODE_LSEEK if no llseek function Jason A. Donenfeld
2022-06-24 17:04 ` Al Viro
2022-06-24 17:09 ` Jason A. Donenfeld
2022-06-24 17:13 ` Al Viro
2022-06-24 17:17 ` Jason A. Donenfeld
2022-06-24 16:56 ` [PATCH 4/6] fs: check FMODE_LSEEK to control internal pipe splicing Jason A. Donenfeld
2022-06-24 16:56 ` [PATCH 5/6] dma-buf: remove useless FMODE_LSEEK flag Jason A. Donenfeld
2022-06-24 21:51 ` Al Viro
2022-06-24 16:56 ` [PATCH 6/6] vfio: do not set " Jason A. Donenfeld
2022-06-24 21:53 ` Al Viro
2022-06-25 10:52 ` Jason A. Donenfeld
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