[PATCH v2 14/25] y2038: Use a common definition for msqid_ds
Adhemerval Zanella
adhemerval.zanella@linaro.org
Mon Jun 7 18:29:49 GMT 2021
On 04/06/2021 16:38, Carlos O'Donell wrote:
> On 5/18/21 4:56 PM, Adhemerval Zanella wrote:
>> From: Lukasz Majewski <lukma@denx.de>
>>
>> Instead of replicate the same definitions from struct_msqid64_ds.h
>> on the multiple struct_msqid_ds.h, use a common header which is included
>> when required (struct_msqid64_ds_helper.h).
>>
>> The __USE_TIME_BITS64 is not defined internally yet, although the
>> internal header is used when building the 64-bit stat implementations.
>
> Requesting a v3 please.
>
> Please add the __glibc_reserved* members to the structures to preserve
> maximum compatibility with the kernel structure.
>
> What I would like to see is that __glibc_reserved4 and __glibc_reserved5
> are *preserved* for both ABIs in the dual-time case. The kernel for msqid
> still has the following:
>
> 26 struct msqid64_ds {
> 27 struct ipc64_perm msg_perm;
> 28 #if __BITS_PER_LONG == 64
> 29 long msg_stime; /* last msgsnd time */
> 30 long msg_rtime; /* last msgrcv time */
> 31 long msg_ctime; /* last change time */
> 32 #else
> 33 unsigned long msg_stime; /* last msgsnd time */
> 34 unsigned long msg_stime_high;
> 35 unsigned long msg_rtime; /* last msgrcv time */
> 36 unsigned long msg_rtime_high;
> 37 unsigned long msg_ctime; /* last change time */
> 38 unsigned long msg_ctime_high;
> 39 #endif
> 40 unsigned long msg_cbytes; /* current number of bytes on queue */
> 41 unsigned long msg_qnum; /* number of messages in queue */
> 42 unsigned long msg_qbytes; /* max number of bytes on queue */
> 43 __kernel_pid_t msg_lspid; /* pid of last msgsnd */
> 44 __kernel_pid_t msg_lrpid; /* last receive pid */
> 45 unsigned long __unused4;
> 46 unsigned long __unused5;
> 47 };
>
> For maximum compatibility with future kernel changes we should keep
> the unused fields in the glibc equivalent structure. If the values are
> ever used then they would already be allocated as part of the size of
> the structure without the need for an ABI change. Given that these are
> somewhat legacy APIs we should be aiming for preserving existing behaviour
> rather than aiming for the smallest possible size structure.
>
> On i686 the new 64-bit time_t struct is only 80 bytes, while the original
> struct size is 88 bytes. Adding the reserved entries brings this back to
> 88 bytes in the new ABI. We can add static asserts if we think we need to
> check exactly for alignment of 64-bit time_t, but since we copy from a
> kernel structure I'm largely worried about the ABI being too small to cary
> the information that we might need to copy from the matching kernel struct.
>
Alright, I already sent my findings that it would increase the msqid_ds
size for _TIME_BITS=64 on some legacy ABIs (arm, mips, s390) but as
we discussed on weekly call it should be fine.
I don't think we need a static assert to check for alignment here (since
glibc export struct for _TIME_BITS might not be potentially equal to
kernel expected one and we already do the heavy lifting in msgctl to
copy and adjust the fields).
>
> This is a spurious cleanup from the last patch IMO. If possible please move it
> into the previous commit.
>
> s/defitions/definitions/g
>
>> Copyright (C) 2021 Free Software Foundation, Inc.
>> This file is part of the GNU C Library.
>>
Ack, I just removed this change.
>> diff --git a/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
>> index 43e8cd7cfc..992734914a 100644
>> --- a/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
>> +++ b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
>> @@ -25,14 +25,6 @@
>> #else
>> struct __msqid64_ds
>> {
>> - struct ipc_perm msg_perm; /* structure describing operation permission */
>> - __time64_t msg_stime; /* time of last msgsnd command */
>> - __time64_t msg_rtime; /* time of last msgsnd command */
>> - __time64_t msg_ctime; /* time of last change */
>> - __syscall_ulong_t __msg_cbytes; /* current number of bytes on queue */
>> - msgqnum_t msg_qnum; /* number of messages currently on queue */
>> - msglen_t msg_qbytes; /* max number of bytes allowed on queue */
>> - __pid_t msg_lspid; /* pid of last msgsnd() */
>> - __pid_t msg_lrpid; /* pid of last msgrcv() */
>> +# include <bits/types/struct_msqid64_ds_helper.h>
>
> OK. Used unconditionally since this is 64-bit time_t.
>
>> };
>> #endif
>> diff --git a/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds_helper.h b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds_helper.h
>> new file mode 100644
>> index 0000000000..02dfddaa2b
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds_helper.h
>> @@ -0,0 +1,28 @@
>> +/* Common defintions for struct msqid_ds with 64 bit time.
>
> s/defintions/definitions/g
Ack.
>
>> + Copyright (C) 2021 Free Software Foundation, Inc.
>> + This file is part of the GNU C Library.
>> +
>> + The GNU C Library is free software; you can redistribute it and/or
>> + modify it under the terms of the GNU Lesser General Public
>> + License as published by the Free Software Foundation; either
>> + version 2.1 of the License, or (at your option) any later version.
>> +
>> + The GNU C Library is distributed in the hope that it will be useful,
>> + but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
>> + Lesser General Public License for more details.
>> +
>> + You should have received a copy of the GNU Lesser General Public
>> + License along with the GNU C Library. If not, see
>> + <https://www.gnu.org/licenses/>. */
>> +
>
> Reviewing...
>
>> + /* Content of internal __msqid64_ds. */
>> + struct ipc_perm msg_perm; /* structure describing operation permission */
>
> OK.
>
>> + __time64_t msg_stime; /* time of last msgsnd command */
>> + __time64_t msg_rtime; /* time of last msgsnd command */
>> + __time64_t msg_ctime; /* time of last change */
>
> OK. Usually a tuple of * and *_high (endian swapping for order applied).
>
>> + __syscall_ulong_t __msg_cbytes; /* current number of bytes on queue */
>
> OK.
>
>> + msgqnum_t msg_qnum; /* number of messages currently on queue */
>
> OK.
>
>> + msglen_t msg_qbytes; /* max number of bytes allowed on queue */
>
> OK.
>
>> + __pid_t msg_lspid; /* pid of last msgsnd() */
>> + __pid_t msg_lrpid; /* pid of last msgrcv() */
>
> OK.
>
> Add __glibc_reserved4/5 entries here.
>
Ack.
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