[PATCH liburing] man/io_uring_enter.2: add notes about direct open/accept

[PATCH liburing] man/io_uring_enter.2: add notes about direct open/accept

[Pavel Begunkov]

Add a few lines describing openat/openat2/accept bypassing normal file
tables and installing files right into the fixed file table.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 man/io_uring_enter.2 | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/man/io_uring_enter.2 b/man/io_uring_enter.2
index 9ccedef..52a5e13 100644
--- a/man/io_uring_enter.2
+++ b/man/io_uring_enter.2
@@ -511,6 +511,18 @@ field. See also
 .BR accept4(2)
 for the general description of the related system call. Available since 5.5.
 
+If the
+.I file_index
+field is set to a non-negative number, the file won't be installed into the
+normal file table as usual but will be placed into the fixed file table at index
+.I file_index - 1.
+In this case, instead of returning a file descriptor, the result will contain
+0 on success or an error. If there is already a file registered at this index,
+the request will fail with
+.B -EBADF.
+
+Available since 5.15.
+
 .TP
 .B IORING_OP_ASYNC_CANCEL
 Attempt to cancel an already issued request.
@@ -634,6 +646,18 @@ is access mode of the file. See also
 .BR openat(2)
 for the general description of the related system call. Available since 5.6.
 
+If the
+.I file_index
+field is set to a non-negative number, the file won't be installed into the
+normal file table as usual but will be placed into the fixed file table at index
+.I file_index - 1.
+In this case, instead of returning a file descriptor, the result will contain
+0 on success or an error. If there is already a file registered at this index,
+the request will fail with
+.B -EBADF.
+
+Available since 5.15.
+
 .TP
 .B IORING_OP_OPENAT2
 Issue the equivalent of a
@@ -654,6 +678,18 @@ should be set to the address of the open_how structure. See also
 .BR openat2(2)
 for the general description of the related system call. Available since 5.6.
 
+If the
+.I file_index
+field is set to a non-negative number, the file won't be installed into the
+normal file table as usual but will be placed into the fixed file table at index
+.I file_index - 1.
+In this case, instead of returning a file descriptor, the result will contain
+0 on success or an error. If there is already a file registered at this index,
+the request will fail with
+.B -EBADF.
+
+Available since 5.15.
+
 .TP
 .B IORING_OP_CLOSE
 Issue the equivalent of a
-- 
2.33.0

Re: [PATCH liburing] man/io_uring_enter.2: add notes about direct open/accept

[Jens Axboe]

On 8/31/21 1:52 PM, Pavel Begunkov wrote:
> Add a few lines describing openat/openat2/accept bypassing normal file
> tables and installing files right into the fixed file table.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  man/io_uring_enter.2 | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/man/io_uring_enter.2 b/man/io_uring_enter.2
> index 9ccedef..52a5e13 100644
> --- a/man/io_uring_enter.2
> +++ b/man/io_uring_enter.2
> @@ -511,6 +511,18 @@ field. See also
>  .BR accept4(2)
>  for the general description of the related system call. Available since 5.5.
>  
> +If the
> +.I file_index
> +field is set to a non-negative number, the file won't be installed into the
> +normal file table as usual but will be placed into the fixed file table at index
> +.I file_index - 1.
> +In this case, instead of returning a file descriptor, the result will contain
> +0 on success or an error. If there is already a file registered at this index,

I don't think non-negative is correct, it has to be set to a positive
number. non-negative would include 0, which isn't correct.

Should also include a note on if these types of file are used, they
won't work in anything but io_uring. That's obvious to us, but should be
noted that they then only live within the realm of the ring itself, not
the system as a whole.

-- 
Jens Axboe

Re: [PATCH liburing] man/io_uring_enter.2: add notes about direct open/accept

[Pavel Begunkov]

On 8/31/21 9:04 PM, Jens Axboe wrote:
> On 8/31/21 1:52 PM, Pavel Begunkov wrote:
>> Add a few lines describing openat/openat2/accept bypassing normal file
>> tables and installing files right into the fixed file table.
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>  man/io_uring_enter.2 | 36 ++++++++++++++++++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>
>> diff --git a/man/io_uring_enter.2 b/man/io_uring_enter.2
>> index 9ccedef..52a5e13 100644
>> --- a/man/io_uring_enter.2
>> +++ b/man/io_uring_enter.2
>> @@ -511,6 +511,18 @@ field. See also
>>  .BR accept4(2)
>>  for the general description of the related system call. Available since 5.5.
>>  
>> +If the
>> +.I file_index
>> +field is set to a non-negative number, the file won't be installed into the
>> +normal file table as usual but will be placed into the fixed file table at index
>> +.I file_index - 1.
>> +In this case, instead of returning a file descriptor, the result will contain
>> +0 on success or an error. If there is already a file registered at this index,
> 
> I don't think non-negative is correct, it has to be set to a positive
> number. non-negative would include 0, which isn't correct.

Oh, right, should have been non-zero

> Should also include a note on if these types of file are used, they
> won't work in anything but io_uring. That's obvious to us, but should be
> noted that they then only live within the realm of the ring itself, not
> the system as a whole.

Will send a v2


-- 
Pavel Begunkov