From: Ian Kent <raven@themaw.net>
To: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
autofs mailing list <autofs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Kernel Mailing List <linux-kernel@vger.kernel.org>,
Bill O'Donnell <billodo@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 7/8] autofs: convert autofs to use the new mount api
Date: Tue, 26 Sep 2023 14:53:17 +0800 [thread overview]
Message-ID: <ce5106f6-08ee-43e7-6239-6a46992649d4@themaw.net> (raw)
In-Reply-To: <7121dcf7-23fe-07a5-9df4-9ea7af6f5964@themaw.net>
On 22/9/23 21:27, Ian Kent wrote:
> On 22/9/23 19:59, Christian Brauner wrote:
>>> + fsparam_fd ("fd", Opt_fd),
>>> +/*
>>> + * Open the fd. We do it here rather than in get_tree so that it's
>>> done in the
>>> + * context of the system call that passed the data and not the one
>>> that
>>> + * triggered the superblock creation, lest the fd gets reassigned.
>>> + */
>>> +static int autofs_parse_fd(struct fs_context *fc, int fd)
>>> {
>>> + struct autofs_sb_info *sbi = fc->s_fs_info;
>>> struct file *pipe;
>>> int ret;
>>> pipe = fget(fd);
>>> if (!pipe) {
>>> - pr_err("could not open pipe file descriptor\n");
>>> + errorf(fc, "could not open pipe file descriptor");
>>> return -EBADF;
>>> }
>>> ret = autofs_check_pipe(pipe);
>>> if (ret < 0) {
>>> - pr_err("Invalid/unusable pipe\n");
>>> + errorf(fc, "Invalid/unusable pipe");
>>> fput(pipe);
>>> return -EBADF;
>>> }
>>> +static int autofs_parse_param(struct fs_context *fc, struct
>>> fs_parameter *param)
>>> {
>>> + return autofs_parse_fd(fc, result.int_32);
>> Mah, so there's a difference between the new and the old mount api
>> that we
>> should probably hide on the VFS level for fsparam_fd. Basically, if
>> you're
>> coming through the new mount api via fsconfig(FSCONFIG_SET_FD, fd)
>> then the vfs
>> will have done param->file = fget(fd) for you already so there's no
>> need to
>> call fget() again. We can just take ownership of the reference that
>> the vfs
>> took for us.
>>
>> But if we're coming in through the old mount api then we need to call
>> fget.
>> There's nothing wrong with your code but it doesn't take advantage of
>> the new
>> mount api which would be unfortunate. So I folded a small extension
>> into this
>> see [1].
>>
>> There's an unrelated bug in fs_param_is_fd() that I'm also fixing see
>> [2].
>
> Ok, that's interesting, I'll have a look at these developments tomorrow,
>
> admittedly (obviously) I hadn't looked at the code for some time ...
This code pattern is a bit unusual, it looks a bit untidy to have different
behavior between the two but I expect there was a reason to include the fd
handling and have this small difference anyway ...
In [2] that's a good catch, I certainly was caught by it, ;(
>
>
> Ian
>
>>
>> I've tested both changes with the old and new mount api.
>>
>> [1]:
>> diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
>> index 3f2dfed428f9..0477bce7d277 100644
>> --- a/fs/autofs/inode.c
>> +++ b/fs/autofs/inode.c
>> @@ -150,13 +150,20 @@ struct autofs_fs_context {
>> * context of the system call that passed the data and not the one
>> that
>> * triggered the superblock creation, lest the fd gets reassigned.
>> */
>> -static int autofs_parse_fd(struct fs_context *fc, int fd)
>> +static int autofs_parse_fd(struct fs_context *fc, struct
>> autofs_sb_info *sbi,
>> + struct fs_parameter *param,
>> + struct fs_parse_result *result)
>> {
>> - struct autofs_sb_info *sbi = fc->s_fs_info;
>> struct file *pipe;
>> int ret;
>>
>> - pipe = fget(fd);
>> + if (param->type == fs_value_is_file) {
>> + /* came through the new api */
>> + pipe = param->file;
>> + param->file = NULL;
>> + } else {
>> + pipe = fget(result->uint_32);
>> + }
>> if (!pipe) {
>> errorf(fc, "could not open pipe file descriptor");
>> return -EBADF;
>> @@ -165,14 +172,15 @@ static int autofs_parse_fd(struct fs_context
>> *fc, int fd)
>> ret = autofs_check_pipe(pipe);
>> if (ret < 0) {
>> errorf(fc, "Invalid/unusable pipe");
>> - fput(pipe);
>> + if (param->type != fs_value_is_file)
>> + fput(pipe);
>> return -EBADF;
>> }
>>
>> if (sbi->pipe)
>> fput(sbi->pipe);
>>
>> - sbi->pipefd = fd;
>> + sbi->pipefd = result->uint_32;
>> sbi->pipe = pipe;
>>
>> return 0;
>>
>> [2]:
>> From 2f9171200505c82e744a235c85377e36ed190109 Mon Sep 17 00:00:00 2001
>> From: Christian Brauner <brauner@kernel.org>
>> Date: Fri, 22 Sep 2023 13:49:05 +0200
>> Subject: [PATCH] fsconfig: ensure that dirfd is set to aux
>>
>> The code in fs_param_is_fd() expects param->dirfd to be set to the fd
>> that was used to set param->file to initialize result->uint_32. So make
>> sure it's set so users like autofs using FSCONFIG_SET_FD with the new
>> mount api can rely on this to be set to the correct value.
>>
>> Signed-off-by: Christian Brauner <brauner@kernel.org>
>> ---
>> fs/fsopen.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/fsopen.c b/fs/fsopen.c
>> index ce03f6521c88..6593ae518115 100644
>> --- a/fs/fsopen.c
>> +++ b/fs/fsopen.c
>> @@ -465,6 +465,7 @@ SYSCALL_DEFINE5(fsconfig,
>> param.file = fget(aux);
>> if (!param.file)
>> goto out_key;
>> + param.dirfd = aux;
>> break;
>> default:
>> break;
next prev parent reply other threads:[~2023-09-26 6:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-22 4:12 [PATCH 0/8] autofs - convert to to use mount api Ian Kent
2023-09-22 4:12 ` [PATCH 1/8] autofs: refactor autofs_prepare_pipe() Ian Kent
2023-09-22 4:12 ` [PATCH 2/8] autofs: add autofs_parse_fd() Ian Kent
2023-09-22 4:12 ` [PATCH 3/8] autofs: refactor super block info init Ian Kent
2023-09-22 4:12 ` [PATCH 4/8] autofs: reformat 0pt enum declaration Ian Kent
2023-09-22 4:12 ` [PATCH 5/8] autofs: refactor parse_options() Ian Kent
2023-09-22 4:12 ` [PATCH 6/8] autofs: validate protocol version Ian Kent
2023-09-22 4:12 ` [PATCH 7/8] autofs: convert autofs to use the new mount api Ian Kent
2023-09-22 8:31 ` Christian Brauner
2023-09-22 9:33 ` Ian Kent
2023-09-22 11:59 ` Christian Brauner
2023-09-22 13:27 ` Ian Kent
2023-09-26 6:53 ` Ian Kent [this message]
2023-09-22 4:12 ` [PATCH 8/8] autofs: fix protocol sub version setting Ian Kent
2023-09-22 12:11 ` [PATCH 0/8] autofs - convert to to use mount api Christian Brauner
2023-09-22 13:25 ` Bill O'Donnell
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