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Message-ID: <85f24359-47b8-4d62-9fe1-4c29e1767db3@gmail.com>
Date: Thu, 27 Aug 2026 17:49:50 +0200
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Subject: Re: BUG #19369: Not documented that io_uring on kernel versions
 between 5.1 and below 5.6 does not work
To: surya poondla <suryapoondla4@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, "Si, Evan" <evsi@amazon.com>,
 "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>,
 Laurenz Albe <laurenz.albe@cybertec.at>
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From: Pierre Forstmann <pierre.forstmann@gmail.com>
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Hi Surya,

I confirm that the compiler warning is fixed in patch v4.

About testing with meson I use following commands:

# make check
meson test -C build --print-errorlogs --suite setup --suite regress
# make installcheck-world
meson test -C build -q --print-errorlogs --setup running

I have used Ubuntu 2004 to reproduce the issue with Linux kernel 5.4.

After applying the patch and setting io_method=io_uring ,I have checked 
that PG cannot be restarted:

2026-08-27 14:54:13.787 UTC [98714] FATAL:  kernel does not support 
required io_uring operations
2026-08-27 14:54:13.787 UTC [98714] DETAIL:  The kernel supports 
io_uring but lacks one or more of the required opcodes (IORING_OP_READ, 
IORING_OP_WRITE, IORING_OP_READV, IORING_OP_WRITEV). This typically 
occurs on Linux kernels older than 5.6.
2026-08-27 14:54:13.787 UTC [98714] HINT:  Either upgrade your kernel to 
version 5.6 or newer, or use io_method=worker.
2026-08-27 14:54:13.788 UTC [98714] LOG:  database system is shut down

I have checked this with building PG with make and with meson.

I have also reviewed the source code and I have question about following 
code section:

#ifdef HAVE_IO_URING_OPCODE_SUPPORTED
         /*
          * Use io_uring_opcode_supported() if available (liburing 2.1+).
          * This directly queries the kernel for opcode support.
          *
          * PostgreSQL uses both single-buffer (READ/WRITE) and vectored
          * (READV/WRITEV) operations. READV/WRITEV were added in kernel 
5.1,
          * but READ/WRITE were added in kernel 5.6. Check for all four to
          * ensure complete support.
          */
         if (!io_uring_opcode_supported(&test_ring, IORING_OP_READ) ||
                 !io_uring_opcode_supported(&test_ring, IORING_OP_WRITE) ||
                 !io_uring_opcode_supported(&test_ring, IORING_OP_READV) ||
                 !io_uring_opcode_supported(&test_ring, IORING_OP_WRITEV))
         {
                 unsupported = true;
         }
#else


I have tried to compile the routine "is_uring_read_write_unsupported" 
in  a standalone executable and I get following errors:

taio.c: In function ‘is_uring_read_write_unsupported’:
taio.c:63:40: error: passing argument 1 of ‘io_uring_opcode_supported’ 
from incompatible pointer type [-Wincompatible-pointer-types]
    63 |         if (!io_uring_opcode_supported(&test_ring, 
IORING_OP_READ) ||
       |                                        ^~~~~~~~~~
       |                                        |
       |                                        struct io_uring *
In file included from taio.c:16:
/usr/include/liburing.h:153:74: note: expected ‘const struct 
io_uring_probe *’ but argument is of type ‘struct io_uring *’
   153 | IOURINGINLINE int io_uring_opcode_supported(const struct 
io_uring_probe *p,
       |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
taio.c:64:44: error: passing argument 1 of ‘io_uring_opcode_supported’ 
from incompatible pointer type [-Wincompatible-pointer-types]
    64 |  !io_uring_opcode_supported(&test_ring, IORING_OP_WRITE) ||
       |                                            ^~~~~~~~~~
       |                                            |
       |                                            struct io_uring *
/usr/include/liburing.h:153:74: note: expected ‘const struct 
io_uring_probe *’ but argument is of type ‘struct io_uring *’
   153 | IOURINGINLINE int io_uring_opcode_supported(const struct 
io_uring_probe *p,
       |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
taio.c:65:44: error: passing argument 1 of ‘io_uring_opcode_supported’ 
from incompatible pointer type [-Wincompatible-pointer-types]
    65 |  !io_uring_opcode_supported(&test_ring, IORING_OP_READV) ||
       |                                            ^~~~~~~~~~
       |                                            |
       |                                            struct io_uring *
/usr/include/liburing.h:153:74: note: expected ‘const struct 
io_uring_probe *’ but argument is of type ‘struct io_uring *’
   153 | IOURINGINLINE int io_uring_opcode_supported(const struct 
io_uring_probe *p,
       |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
taio.c:66:44: error: passing argument 1 of ‘io_uring_opcode_supported’ 
from incompatible pointer type [-Wincompatible-pointer-types]
    66 |  !io_uring_opcode_supported(&test_ring, IORING_OP_WRITEV))
       |                                            ^~~~~~~~~~
       |                                            |
       |                                            struct io_uring *
/usr/include/liburing.h:153:74: note: expected ‘const struct 
io_uring_probe *’ but argument is of type ‘struct io_uring *’
   153 | IOURINGINLINE int io_uring_opcode_supported(const struct 
io_uring_probe *p,
       |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^

I get these errors both with Debian 13 and Ubuntu 2004.

Can you double-check if this is the right way to call 
io_uring_opcode_support and/or if there is an issue with make/meson 
configuration ?

Regards,

PF


Le 27/08/2026 à 01:28, surya poondla a écrit :
> Hi Pierre,
>
> Thank you for the review.
>
> I fixed the compiler warning in v4.
>
>     I also would like to know if you manage to run the equivalent of
>     'make installcheck-world" with meson ?
>
>
> I couldn't either. I noticed the "meson test --setup running" was 
> running SQL suites (regress, isolation) only and  not the TAP suite.
> So it does not look equivalent to installcheck-world in any case.
>
> I am doing some additional testing and will update my findings.
>
> Regards,
> Surya Poondla
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    <p><font face="monospace">Hi Surya,</font></p>
    <p><font face="monospace">I confirm that the compiler warning is
        fixed in patch v4.</font></p>
    <p><font face="monospace">About testing with meson I use following
        commands:</font></p>
    <p><font face="monospace"># make check<br>
        meson test -C build --print-errorlogs --suite setup --suite
        regress<br>
        # make installcheck-world<br>
        meson test -C build -q --print-errorlogs --setup running</font></p>
    <p><font face="monospace">I have used Ubuntu 2004 to reproduce the
        issue with Linux kernel 5.4.</font></p>
    <p><font face="monospace">After applying the patch and setting
        io_method=io_uring ,I have checked that PG cannot be restarted:</font></p>
    <p><font face="monospace">2026-08-27 14:54:13.787 UTC [98714]
        FATAL:  kernel does not support required io_uring operations<br>
        2026-08-27 14:54:13.787 UTC [98714] DETAIL:  The kernel supports
        io_uring but lacks one or more of the required opcodes
        (IORING_OP_READ, IORING_OP_WRITE, IORING_OP_READV,
        IORING_OP_WRITEV). This typically occurs on Linux kernels older
        than 5.6.<br>
        2026-08-27 14:54:13.787 UTC [98714] HINT:  Either upgrade your
        kernel to version 5.6 or newer, or use io_method=worker.<br>
        2026-08-27 14:54:13.788 UTC [98714] LOG:  database system is
        shut down</font></p>
    <p><font face="monospace">I have checked this with building PG with
        make and with meson.</font></p>
    <p><font face="monospace">I have also reviewed the source code and I
        have question about following code section:</font></p>
    <p><font face="monospace">#ifdef HAVE_IO_URING_OPCODE_SUPPORTED<br>
                /*<br>
                 * Use io_uring_opcode_supported() if available
        (liburing 2.1+).<br>
                 * This directly queries the kernel for opcode support.<br>
                 *<br>
                 * PostgreSQL uses both single-buffer (READ/WRITE) and
        vectored<br>
                 * (READV/WRITEV) operations. READV/WRITEV were added in
        kernel 5.1,<br>
                 * but READ/WRITE were added in kernel 5.6. Check for
        all four to<br>
                 * ensure complete support.<br>
                 */<br>
                if (!io_uring_opcode_supported(&amp;test_ring,
        IORING_OP_READ) ||<br>
                        !io_uring_opcode_supported(&amp;test_ring,
        IORING_OP_WRITE) ||<br>
                        !io_uring_opcode_supported(&amp;test_ring,
        IORING_OP_READV) ||<br>
                        !io_uring_opcode_supported(&amp;test_ring,
        IORING_OP_WRITEV))<br>
                {<br>
                        unsupported = true;<br>
                }<br>
        #else</font></p>
    <p><font face="monospace"><br>
      </font></p>
    <p><font face="monospace">I have tried to compile the routine
        "is_uring_read_write_unsupported" in  a standalone executable
        and I get following errors:</font></p>
    <p><font face="monospace">taio.c: In function
        ‘is_uring_read_write_unsupported’:<br>
        taio.c:63:40: error: passing argument 1 of
        ‘io_uring_opcode_supported’ from incompatible pointer type
        [-Wincompatible-pointer-types]<br>
           63 |         if (!io_uring_opcode_supported(&amp;test_ring,
        IORING_OP_READ) ||<br>
              |                                        ^~~~~~~~~~<br>
              |                                        |<br>
              |                                        struct io_uring *<br>
        In file included from taio.c:16:<br>
        /usr/include/liburing.h:153:74: note: expected ‘const struct
        io_uring_probe *’ but argument is of type ‘struct io_uring *’<br>
          153 | IOURINGINLINE int io_uring_opcode_supported(const struct
        io_uring_probe *p,<br>
              |                                           
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^<br>
        taio.c:64:44: error: passing argument 1 of
        ‘io_uring_opcode_supported’ from incompatible pointer type
        [-Wincompatible-pointer-types]<br>
           64 |               
         !io_uring_opcode_supported(&amp;test_ring, IORING_OP_WRITE) ||<br>
              |                                            ^~~~~~~~~~<br>
              |                                            |<br>
              |                                            struct
        io_uring *<br>
        /usr/include/liburing.h:153:74: note: expected ‘const struct
        io_uring_probe *’ but argument is of type ‘struct io_uring *’<br>
          153 | IOURINGINLINE int io_uring_opcode_supported(const struct
        io_uring_probe *p,<br>
              |                                           
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^<br>
        taio.c:65:44: error: passing argument 1 of
        ‘io_uring_opcode_supported’ from incompatible pointer type
        [-Wincompatible-pointer-types]<br>
           65 |               
         !io_uring_opcode_supported(&amp;test_ring, IORING_OP_READV) ||<br>
              |                                            ^~~~~~~~~~<br>
              |                                            |<br>
              |                                            struct
        io_uring *<br>
        /usr/include/liburing.h:153:74: note: expected ‘const struct
        io_uring_probe *’ but argument is of type ‘struct io_uring *’<br>
          153 | IOURINGINLINE int io_uring_opcode_supported(const struct
        io_uring_probe *p,<br>
              |                                           
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^<br>
        taio.c:66:44: error: passing argument 1 of
        ‘io_uring_opcode_supported’ from incompatible pointer type
        [-Wincompatible-pointer-types]<br>
           66 |               
         !io_uring_opcode_supported(&amp;test_ring, IORING_OP_WRITEV))<br>
              |                                            ^~~~~~~~~~<br>
              |                                            |<br>
              |                                            struct
        io_uring *<br>
        /usr/include/liburing.h:153:74: note: expected ‘const struct
        io_uring_probe *’ but argument is of type ‘struct io_uring *’<br>
          153 | IOURINGINLINE int io_uring_opcode_supported(const struct
        io_uring_probe *p,<br>
              |                                           
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^<br>
      </font></p>
    <p><font face="monospace">I get these errors both with Debian 13 and
        Ubuntu 2004.</font></p>
    <p><font face="monospace">Can you double-check if this is the right
        way to call io_uring_opcode_support and/or if there is an issue
        with make/meson configuration ?</font></p>
    <p><font face="monospace">Regards,</font></p>
    <p><font face="monospace">PF</font></p>
    <p><font face="monospace"><br>
      </font></p>
    <p><font face="monospace"><br>
      </font></p>
    <div class="moz-cite-prefix">Le 27/08/2026 à 01:28, surya poondla a
      écrit :<br>
    </div>
    <blockquote type="cite"
cite="mid:CAOVWO5oVccTRo9RsJvjMCRuBppu_R5Azo+-dq0cQyhds5_4XXw@mail.gmail.com">
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      <div dir="ltr">
        <div dir="ltr">Hi Pierre,<br>
          <br>
          Thank you for the review.<br>
          <br>
          I fixed the compiler warning in v4.<br>
          <br>
        </div>
        <div class="gmail_quote gmail_quote_container">
          <blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I
            also would like to know if you manage to run the equivalent
            of 'make installcheck-world" with meson ?</blockquote>
          <div><br>
            I couldn't either. I noticed the "meson test --setup
            running" was running SQL suites (regress, isolation) only
            and  not the TAP suite. </div>
          <div><span style="background-color:transparent">So it does </span><span
              style="background-color:transparent">not look equivalent
              to installcheck-world in any case.<br>
              <br>
              I am doing some additional testing and will update my
              findings.<br>
              <br>
              Regards,<br>
              Surya Poondla</span></div>
        </div>
      </div>
    </blockquote>
  </body>
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