On Tue, Mar 04, 2025 at 05:25:35PM +0530, Ritesh Harjani (IBM) wrote:
> preadv2() was introduced in Linux 4.6. This patch adds support for
> preadv2() to xfs_io.
>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
> ---
> configure.ac | 1 +
> include/builddefs.in | 1 +
> io/Makefile | 4 ++++
> io/pread.c | 45 ++++++++++++++++++++++++++++---------------
> m4/package_libcdev.m4 | 18 +++++++++++++++++
> 5 files changed, 54 insertions(+), 15 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index 8c76f398..658117ad 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -153,6 +153,7 @@ AC_PACKAGE_NEED_URCU_H
> AC_PACKAGE_NEED_RCU_INIT
>
> AC_HAVE_PWRITEV2
> +AC_HAVE_PREADV2
I wonder, will we ever encounter a C library that has pwritev2 and /not/
preadv2?
> AC_HAVE_COPY_FILE_RANGE
> AC_NEED_INTERNAL_FSXATTR
> AC_NEED_INTERNAL_FSCRYPT_ADD_KEY_ARG
> diff --git a/include/builddefs.in b/include/builddefs.in
> index 82840ec7..a11d201c 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -94,6 +94,7 @@ ENABLE_SCRUB = @enable_scrub@
> HAVE_ZIPPED_MANPAGES = @have_zipped_manpages@
>
> HAVE_PWRITEV2 = @have_pwritev2@
> +HAVE_PREADV2 = @have_preadv2@
> HAVE_COPY_FILE_RANGE = @have_copy_file_range@
> NEED_INTERNAL_FSXATTR = @need_internal_fsxattr@
> NEED_INTERNAL_FSCRYPT_ADD_KEY_ARG = @need_internal_fscrypt_add_key_arg@
> diff --git a/io/Makefile b/io/Makefile
> index 8f835ec7..f8b19ac5 100644
> --- a/io/Makefile
> +++ b/io/Makefile
> @@ -69,6 +69,10 @@ ifeq ($(HAVE_PWRITEV2),yes)
> LCFLAGS += -DHAVE_PWRITEV2
> endif
>
> +ifeq ($(HAVE_PREADV2),yes)
> +LCFLAGS += -DHAVE_PREADV2
> +endif
> +
> ifeq ($(HAVE_MAP_SYNC),yes)
> LCFLAGS += -DHAVE_MAP_SYNC
> endif
> diff --git a/io/pread.c b/io/pread.c
> index 62c771fb..782f2a36 100644
> --- a/io/pread.c
> +++ b/io/pread.c
> @@ -162,7 +162,8 @@ static ssize_t
> do_preadv(
> int fd,
> off_t offset,
> - long long count)
> + long long count,
> + int preadv2_flags)
Nit: ^ space before tab. There's a bunch more of thense, every
time a "preadv2_flags" variable or parameter are declared.
> {
> int vecs = 0;
> ssize_t oldlen = 0;
> @@ -181,8 +182,14 @@ do_preadv(
> } else {
> vecs = vectors;
> }
> +#ifdef HAVE_PREADV2
> + if (preadv2_flags)
> + bytes = preadv2(fd, iov, vectors, offset, preadv2_flags);
> + else
> + bytes = preadv(fd, iov, vectors, offset);
> +#else
> bytes = preadv(fd, iov, vectors, offset);
> -
> +#endif
Can we have the case that preadv2_flags!=0 and HAVE_PREADV2 isn't
defined? If so, then there ought to be a warning about that.
--D
> /* restore trimmed iov */
> if (oldlen)
> iov[vecs - 1].iov_len = oldlen;
> @@ -195,12 +202,13 @@ do_pread(
> int fd,
> off_t offset,
> long long count,
> - size_t buffer_size)
> + size_t buffer_size,
> + int preadv2_flags)
> {
> if (!vectors)
> return pread(fd, io_buffer, min(count, buffer_size), offset);
>
> - return do_preadv(fd, offset, count);
> + return do_preadv(fd, offset, count, preadv2_flags);
> }
>
> static int
> @@ -210,7 +218,8 @@ read_random(
> long long count,
> long long *total,
> unsigned int seed,
> - int eof)
> + int eof,
> + int preadv2_flags)
> {
> off_t end, off, range;
> ssize_t bytes;
> @@ -234,7 +243,7 @@ read_random(
> io_buffersize;
> else
> off = offset;
> - bytes = do_pread(fd, off, io_buffersize, io_buffersize);
> + bytes = do_pread(fd, off, io_buffersize, io_buffersize, preadv2_flags);
> if (bytes == 0)
> break;
> if (bytes < 0) {
> @@ -256,7 +265,8 @@ read_backward(
> off_t *offset,
> long long *count,
> long long *total,
> - int eof)
> + int eof,
> + int preadv2_flags)
> {
> off_t end, off = *offset;
> ssize_t bytes = 0, bytes_requested;
> @@ -276,7 +286,7 @@ read_backward(
> /* Do initial unaligned read if needed */
> if ((bytes_requested = (off % io_buffersize))) {
> off -= bytes_requested;
> - bytes = do_pread(fd, off, bytes_requested, io_buffersize);
> + bytes = do_pread(fd, off, bytes_requested, io_buffersize, preadv2_flags);
> if (bytes == 0)
> return ops;
> if (bytes < 0) {
> @@ -294,7 +304,7 @@ read_backward(
> while (cnt > end) {
> bytes_requested = min(cnt, io_buffersize);
> off -= bytes_requested;
> - bytes = do_pread(fd, off, cnt, io_buffersize);
> + bytes = do_pread(fd, off, cnt, io_buffersize, preadv2_flags);
> if (bytes == 0)
> break;
> if (bytes < 0) {
> @@ -318,14 +328,15 @@ read_forward(
> long long *total,
> int verbose,
> int onlyone,
> - int eof)
> + int eof,
> + int preadv2_flags)
> {
> ssize_t bytes;
> int ops = 0;
>
> *total = 0;
> while (count > 0 || eof) {
> - bytes = do_pread(fd, offset, count, io_buffersize);
> + bytes = do_pread(fd, offset, count, io_buffersize, preadv2_flags);
> if (bytes == 0)
> break;
> if (bytes < 0) {
> @@ -353,7 +364,7 @@ read_buffer(
> int verbose,
> int onlyone)
> {
> - return read_forward(fd, offset, count, total, verbose, onlyone, 0);
> + return read_forward(fd, offset, count, total, verbose, onlyone, 0, 0);
> }
>
> static int
> @@ -371,6 +382,7 @@ pread_f(
> int Cflag, qflag, uflag, vflag;
> int eof = 0, direction = IO_FORWARD;
> int c;
> + int preadv2_flags = 0;
>
> Cflag = qflag = uflag = vflag = 0;
> init_cvtnum(&fsblocksize, &fssectsize);
> @@ -463,15 +475,18 @@ pread_f(
> case IO_RANDOM:
> if (!zeed) /* srandom seed */
> zeed = time(NULL);
> - c = read_random(file->fd, offset, count, &total, zeed, eof);
> + c = read_random(file->fd, offset, count, &total, zeed, eof,
> + preadv2_flags);
> break;
> case IO_FORWARD:
> - c = read_forward(file->fd, offset, count, &total, vflag, 0, eof);
> + c = read_forward(file->fd, offset, count, &total, vflag, 0, eof,
> + preadv2_flags);
> if (eof)
> count = total;
> break;
> case IO_BACKWARD:
> - c = read_backward(file->fd, &offset, &count, &total, eof);
> + c = read_backward(file->fd, &offset, &count, &total, eof,
> + preadv2_flags);
> break;
> default:
> ASSERT(0);
> diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
> index 4ef7e8f6..5a1f748a 100644
> --- a/m4/package_libcdev.m4
> +++ b/m4/package_libcdev.m4
> @@ -16,6 +16,24 @@ pwritev2(0, 0, 0, 0, 0);
> AC_SUBST(have_pwritev2)
> ])
>
> +#
> +# Check if we have a preadv2 libc call (Linux)
> +#
> +AC_DEFUN([AC_HAVE_PREADV2],
> + [ AC_MSG_CHECKING([for preadv2])
> + AC_LINK_IFELSE(
> + [ AC_LANG_PROGRAM([[
> +#define _GNU_SOURCE
> +#include <sys/uio.h>
> + ]], [[
> +preadv2(0, 0, 0, 0, 0);
> + ]])
> + ], have_preadv2=yes
> + AC_MSG_RESULT(yes),
> + AC_MSG_RESULT(no))
> + AC_SUBST(have_preadv2)
> + ])
> +
> #
> # Check if we have a copy_file_range system call (Linux)
> #
> --
> 2.48.1
>
>
