linux-kernel - Re: [PATCH resend] eventfd: make eventfd files distinguishable in /proc/$PID/fd

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Date:   Wed, 12 Dec 2018 16:57:20 +0900 (JST)
From:   Masatake YAMATO <yamato@...hat.com>
To:     serge@...lyn.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH resend] eventfd: make eventfd files distinguishable in
 /proc/$PID/fd

On Tue, 11 Dec 2018 17:09:14 -0600, "Serge E. Hallyn" <serge@...lyn.com> wrote:
> On Mon, Dec 10, 2018 at 03:35:46AM +0900, Masatake YAMATO wrote:
>> Finding endpoints of an IPC channel is one of essential task to
>> understand how a user program works. Procfs and netlink socket provide
>> enough hints to find endpoints for IPC channels like pipes, unix
>> sockets, and pseudo terminals. However, there is no simple way to find
>> endpoints for an eventfd file from userland. An inode number doesn't
>> hint. Unlike pipe, all eventfd files shares one inode object.
>> 
>> To provide the way to find endpoints of an eventfd file, this patch
>> adds eventfd identifiers to the output of 'ls -l /proc/$pid/fd' like:
>> 
>>   ...
>>   lrwx------. 1 qemu qemu 64 May 20 04:49 93 -> 'anon_inode:[eventfd:130]'
>>   lrwx------. 1 qemu qemu 64 May 20 04:49 94 -> 'anon_inode:[eventfd:131]'
>>   ...
>> 
>> Here "130" and "131" are added as identifiers newly added.
>> In the case that ida_simple_get returns an error, this change doesn't add
>> an identifier; just use "[eventfd]" as before.
>> 
>> Signed-off-by: Masatake YAMATO <yamato@...hat.com>
> 
> I'm going to love this when I need it :)  Thanks.
> 
> Acked-by: Serge Hallyn <serge@...lyn.com>
>

Thank you for replying.
This is the first time getting replying since my first post,
Mon, 21 May 2018 05:18:23 +0900.

Can I expect my patch is merged to the mainline?
Or should I do something more?

Masatake YAMATO

>> ---
>>  fs/eventfd.c | 14 +++++++++++++-
>>  1 file changed, 13 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/eventfd.c b/fs/eventfd.c
>> index 08d3bd602f73..c18952948110 100644
>> --- a/fs/eventfd.c
>> +++ b/fs/eventfd.c
>> @@ -21,6 +21,11 @@
>>  #include <linux/eventfd.h>
>>  #include <linux/proc_fs.h>
>>  #include <linux/seq_file.h>
>> +#include <linux/idr.h>
>> +
>> +/* Worst case buffer size needed for holding an integer. */
>> +#define ITOA_MAX_LEN 12
>> +DEFINE_IDA(eventfd_ida);
>>  
>>  struct eventfd_ctx {
>>  	struct kref kref;
>> @@ -35,6 +40,7 @@ struct eventfd_ctx {
>>  	 */
>>  	__u64 count;
>>  	unsigned int flags;
>> +	int id;
>>  };
>>  
>>  /**
>> @@ -69,6 +75,8 @@ EXPORT_SYMBOL_GPL(eventfd_signal);
>>  
>>  static void eventfd_free_ctx(struct eventfd_ctx *ctx)
>>  {
>> +	if (ctx->id >= 0)
>> +		ida_simple_remove(&eventfd_ida, ctx->id);
>>  	kfree(ctx);
>>  }
>>  
>> @@ -384,6 +392,7 @@ static int do_eventfd(unsigned int count, int flags)
>>  {
>>  	struct eventfd_ctx *ctx;
>>  	int fd;
>> +	char name[1 + 8 + ITOA_MAX_LEN + 1 + 1] = "[eventfd]";
>>  
>>  	/* Check the EFD_* constants for consistency.  */
>>  	BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
>> @@ -400,8 +409,11 @@ static int do_eventfd(unsigned int count, int flags)
>>  	init_waitqueue_head(&ctx->wqh);
>>  	ctx->count = count;
>>  	ctx->flags = flags;
>> +	ctx->id = ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL);
>>  
>> -	fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
>> +	if (ctx->id >= 0)
>> +		snprintf(name, sizeof(name), "[eventfd:%d]", ctx->id);
>> +	fd = anon_inode_getfd(name, &eventfd_fops, ctx,
>>  			      O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
>>  	if (fd < 0)
>>  		eventfd_free_ctx(ctx);
>> -- 
>> 2.17.0