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Date: Tue, 27 Jan 2009 00:42:51 +0100
From: Michael Kerrisk <mtk.manpages@...glemail.com>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
linux-api@...r.kernel.org, aarcange@...hat.com
Subject: Re: [PATCH v7 3/5] Add preadv and pwritev system calls.
Gerd,
On Mon, Jan 26, 2009 at 2:26 PM, Gerd Hoffmann <kraxel@...hat.com> wrote:
> This patch adds preadv and pwritev system calls. These syscalls are a
> pretty straightforward combination of pread and readv (same for write).
> They are quite useful for doing vectored I/O in threaded applications.
> Using lseek+readv instead opens race windows you'll have to plug with
> locking.
>
> Other systems have such system calls too, for example NetBSD, check
> here: http://www.daemon-systems.org/man/preadv.2.html
>
> The application-visible interface provided by glibc should look like
> this to be compatible to the existing implementations in the *BSD family:
>
> ssize_t preadv(int d, const struct iovec *iov, int iovcnt, off_t offset);
> ssize_t pwritev(int d, const struct iovec *iov, int iovcnt, off_t offset);
I earlier asked if you could provide some userspace example code using
this API. If there was a response, I missed it. Could you please
provide some working test using this interface.
Cheers,
Michael
> This prototype has one problem though: On 32bit archs is the (64bit)
> offset argument unaligned, which the syscall ABI of several archs
> doesn't allow to do. At least s390 needs a wrapper in glibc to handle
> this. As we'll need a wrappers in glibc anyway I've decided to push
> problem to glibc entriely and use a syscall prototype which works
> without arch-specific wrappers inside the kernel: The offset argument
> is explicitly splitted into two 32bit values.
>
> The patch sports the actual system call implementation and the windup in
> the x86 system call tables. Other archs follow as separate patches.
>
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
> arch/x86/ia32/ia32entry.S | 2 +
> arch/x86/include/asm/unistd_32.h | 2 +
> arch/x86/include/asm/unistd_64.h | 4 +++
> arch/x86/kernel/syscall_table_32.S | 2 +
> fs/compat.c | 36 ++++++++++++++++++++++++++
> fs/read_write.c | 50 ++++++++++++++++++++++++++++++++++++
> include/linux/compat.h | 6 ++++
> include/linux/syscalls.h | 4 +++
> 8 files changed, 106 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index 256b00b..9a8501b 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -826,4 +826,6 @@ ia32_sys_call_table:
> .quad sys_dup3 /* 330 */
> .quad sys_pipe2
> .quad sys_inotify_init1
> + .quad compat_sys_preadv
> + .quad compat_sys_pwritev
> ia32_syscall_end:
> diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h
> index f2bba78..6e72d74 100644
> --- a/arch/x86/include/asm/unistd_32.h
> +++ b/arch/x86/include/asm/unistd_32.h
> @@ -338,6 +338,8 @@
> #define __NR_dup3 330
> #define __NR_pipe2 331
> #define __NR_inotify_init1 332
> +#define __NR_preadv 333
> +#define __NR_pwritev 334
>
> #ifdef __KERNEL__
>
> diff --git a/arch/x86/include/asm/unistd_64.h b/arch/x86/include/asm/unistd_64.h
> index d2e415e..f818294 100644
> --- a/arch/x86/include/asm/unistd_64.h
> +++ b/arch/x86/include/asm/unistd_64.h
> @@ -653,6 +653,10 @@ __SYSCALL(__NR_dup3, sys_dup3)
> __SYSCALL(__NR_pipe2, sys_pipe2)
> #define __NR_inotify_init1 294
> __SYSCALL(__NR_inotify_init1, sys_inotify_init1)
> +#define __NR_preadv 295
> +__SYSCALL(__NR_preadv, sys_preadv)
> +#define __NR_pwritev 296
> +__SYSCALL(__NR_pwritev, sys_pwritev)
>
>
> #ifndef __NO_STUBS
> diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S
> index e2e86a0..106204c 100644
> --- a/arch/x86/kernel/syscall_table_32.S
> +++ b/arch/x86/kernel/syscall_table_32.S
> @@ -332,3 +332,5 @@ ENTRY(sys_call_table)
> .long sys_dup3 /* 330 */
> .long sys_pipe2
> .long sys_inotify_init1
> + .long sys_preadv
> + .long sys_pwritev
> diff --git a/fs/compat.c b/fs/compat.c
> index 4e65644..1a67eee 100644
> --- a/fs/compat.c
> +++ b/fs/compat.c
> @@ -1204,6 +1204,24 @@ compat_sys_readv(unsigned long fd, const struct compat_iovec __user *vec,
> return ret;
> }
>
> +asmlinkage ssize_t
> +compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low)
> +{
> + loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> + struct file *file;
> + ssize_t ret;
> +
> + if (pos < 0)
> + return -EINVAL;
> + file = fget(fd);
> + if (!file)
> + return -EBADF;
> + ret = compat_readv(file, vec, vlen, &pos);
> + fput(file);
> + return ret;
> +}
> +
> static size_t compat_writev(struct file *file,
> const struct compat_iovec __user *vec,
> unsigned long vlen, loff_t *pos)
> @@ -1241,6 +1259,24 @@ compat_sys_writev(unsigned long fd, const struct compat_iovec __user *vec,
> return ret;
> }
>
> +asmlinkage ssize_t
> +compat_sys_pwritev(unsigned long fd, const struct compat_iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low)
> +{
> + loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> + struct file *file;
> + ssize_t ret;
> +
> + if (pos < 0)
> + return -EINVAL;
> + file = fget(fd);
> + if (!file)
> + return -EBADF;
> + ret = compat_writev(file, vec, vlen, &pos);
> + fput(file);
> + return ret;
> +}
> +
> asmlinkage long
> compat_sys_vmsplice(int fd, const struct compat_iovec __user *iov32,
> unsigned int nr_segs, unsigned int flags)
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 400fe81..6d5d8ff 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -731,6 +731,56 @@ SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
> return ret;
> }
>
> +SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
> + unsigned long, vlen, u32, pos_high, u32, pos_low)
> +{
> + loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> + struct file *file;
> + ssize_t ret = -EBADF;
> + int fput_needed;
> +
> + if (pos < 0)
> + return -EINVAL;
> +
> + file = fget_light(fd, &fput_needed);
> + if (file) {
> + ret = -ESPIPE;
> + if (file->f_mode & FMODE_PREAD)
> + ret = vfs_readv(file, vec, vlen, &pos);
> + fput_light(file, fput_needed);
> + }
> +
> + if (ret > 0)
> + add_rchar(current, ret);
> + inc_syscr(current);
> + return ret;
> +}
> +
> +SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
> + unsigned long, vlen, u32, pos_high, u32, pos_low)
> +{
> + loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> + struct file *file;
> + ssize_t ret = -EBADF;
> + int fput_needed;
> +
> + if (pos < 0)
> + return -EINVAL;
> +
> + file = fget_light(fd, &fput_needed);
> + if (file) {
> + ret = -ESPIPE;
> + if (file->f_mode & FMODE_PWRITE)
> + ret = vfs_writev(file, vec, vlen, &pos);
> + fput_light(file, fput_needed);
> + }
> +
> + if (ret > 0)
> + add_wchar(current, ret);
> + inc_syscw(current);
> + return ret;
> +}
> +
> static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
> size_t count, loff_t max)
> {
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 3fd2194..79dba49 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -183,6 +183,12 @@ asmlinkage ssize_t compat_sys_readv(unsigned long fd,
> const struct compat_iovec __user *vec, unsigned long vlen);
> asmlinkage ssize_t compat_sys_writev(unsigned long fd,
> const struct compat_iovec __user *vec, unsigned long vlen);
> +asmlinkage ssize_t compat_sys_preadv(unsigned long fd,
> + const struct compat_iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low);
> +asmlinkage ssize_t compat_sys_pwritev(unsigned long fd,
> + const struct compat_iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low);
>
> int compat_do_execve(char * filename, compat_uptr_t __user *argv,
> compat_uptr_t __user *envp, struct pt_regs * regs);
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 16875f8..b63e93d 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -456,6 +456,10 @@ asmlinkage long sys_pread64(unsigned int fd, char __user *buf,
> size_t count, loff_t pos);
> asmlinkage long sys_pwrite64(unsigned int fd, const char __user *buf,
> size_t count, loff_t pos);
> +asmlinkage long sys_preadv(unsigned long fd, const struct iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low);
> +asmlinkage long sys_pwritev(unsigned long fd, const struct iovec __user *vec,
> + unsigned long vlen, u32 pos_high, u32 pos_low);
> asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
> asmlinkage long sys_mkdir(const char __user *pathname, int mode);
> asmlinkage long sys_chdir(const char __user *filename);
> --
> 1.6.1
>
> --
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--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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