[PATCH] update the sync.2 man page

[PATCH] update the sync.2 man page

[Christoph Hellwig]

Clarify the description a bit, and document the Linux data integrity
guarantees.

Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/man2/sync.2 b/man2/sync.2
index 5e222cb..28a42c4 100644
--- a/man2/sync.2
+++ b/man2/sync.2
@@ -35,7 +35,7 @@
 .\"
 .TH SYNC 2 2015-08-08 "Linux" "Linux Programmer's Manual"
 .SH NAME
-sync, syncfs \- commit buffer cache to disk
+sync, syncfs \- commit filesystem caches to disk
 .SH SYNOPSIS
 .B #include <unistd.h>
 .sp
@@ -64,8 +64,8 @@ _GNU_SOURCE
 .ad
 .SH DESCRIPTION
 .BR sync ()
-causes all buffered modifications to file metadata and data to be
-written to the underlying filesystems.
+causes all pending modifications to file system metadata and cached file
+data to be written to the underlying filesystems.
 
 .BR syncfs ()
 is like
@@ -108,16 +108,21 @@ In glibc 2.2.1 and earlier,
 it was "int sync(void)", and
 .BR sync ()
 always returned 0.
-.SH BUGS
+
 According to the standard specification (e.g., POSIX.1-2001),
 .BR sync ()
 schedules the writes, but may return before the actual
-writing is done.
-However, since version 1.3.20 Linux does actually wait.
-(This still does not guarantee data integrity: modern disks have
-large caches.)
+writing is done.  However Linux waits for I/O completions,
+and thus
+.BR sync ()
+or
+.BR syncfs ()
+provide the same guarantees as fsync called on every file in
+the system or filesystem respectively.
+.SH BUGS
+Before version 1.3.20 Linux did not wait for I/O to complete
+before returning.
 .SH SEE ALSO
-.BR bdflush (2),
 .BR fdatasync (2),
 .BR fsync (2),
 .BR sync (1)

Re: [PATCH] update the sync.2 man page

[Ross Zwisler]

On Tue, Feb 9, 2016 at 9:21 AM, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
> Clarify the description a bit, and document the Linux data integrity
> guarantees.
>
> Signed-off-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>

Thank you for clarifying this.

> diff --git a/man2/sync.2 b/man2/sync.2
> index 5e222cb..28a42c4 100644
> --- a/man2/sync.2
> +++ b/man2/sync.2
> @@ -35,7 +35,7 @@
>  .\"
>  .TH SYNC 2 2015-08-08 "Linux" "Linux Programmer's Manual"
>  .SH NAME
> -sync, syncfs \- commit buffer cache to disk
> +sync, syncfs \- commit filesystem caches to disk
>  .SH SYNOPSIS
>  .B #include <unistd.h>
>  .sp
> @@ -64,8 +64,8 @@ _GNU_SOURCE
>  .ad
>  .SH DESCRIPTION
>  .BR sync ()
> -causes all buffered modifications to file metadata and data to be
> -written to the underlying filesystems.
> +causes all pending modifications to file system metadata and cached file
> +data to be written to the underlying filesystems.
>
>  .BR syncfs ()
>  is like
> @@ -108,16 +108,21 @@ In glibc 2.2.1 and earlier,
>  it was "int sync(void)", and
>  .BR sync ()
>  always returned 0.
> -.SH BUGS
> +
>  According to the standard specification (e.g., POSIX.1-2001),
>  .BR sync ()
>  schedules the writes, but may return before the actual
> -writing is done.
> -However, since version 1.3.20 Linux does actually wait.
> -(This still does not guarantee data integrity: modern disks have
> -large caches.)
> +writing is done.  However Linux waits for I/O completions,
> +and thus
> +.BR sync ()
> +or
> +.BR syncfs ()
> +provide the same guarantees as fsync called on every file in
> +the system or filesystem respectively.
> +.SH BUGS
> +Before version 1.3.20 Linux did not wait for I/O to complete
> +before returning.
>  .SH SEE ALSO
> -.BR bdflush (2),
>  .BR fdatasync (2),
>  .BR fsync (2),
>  .BR sync (1)
> --
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Re: [PATCH] update the sync.2 man page

[Michael Kerrisk (man-pages)]

On 02/09/2016 05:21 PM, Christoph Hellwig wrote:
> Clarify the description a bit, and document the Linux data integrity
> guarantees.

Thanks, Christoph. Applied.

Cheers,

Michael

> Signed-off-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
> 
> diff --git a/man2/sync.2 b/man2/sync.2
> index 5e222cb..28a42c4 100644
> --- a/man2/sync.2
> +++ b/man2/sync.2
> @@ -35,7 +35,7 @@
>  .\"
>  .TH SYNC 2 2015-08-08 "Linux" "Linux Programmer's Manual"
>  .SH NAME
> -sync, syncfs \- commit buffer cache to disk
> +sync, syncfs \- commit filesystem caches to disk
>  .SH SYNOPSIS
>  .B #include <unistd.h>
>  .sp
> @@ -64,8 +64,8 @@ _GNU_SOURCE
>  .ad
>  .SH DESCRIPTION
>  .BR sync ()
> -causes all buffered modifications to file metadata and data to be
> -written to the underlying filesystems.
> +causes all pending modifications to file system metadata and cached file
> +data to be written to the underlying filesystems.
>  
>  .BR syncfs ()
>  is like
> @@ -108,16 +108,21 @@ In glibc 2.2.1 and earlier,
>  it was "int sync(void)", and
>  .BR sync ()
>  always returned 0.
> -.SH BUGS
> +
>  According to the standard specification (e.g., POSIX.1-2001),
>  .BR sync ()
>  schedules the writes, but may return before the actual
> -writing is done.
> -However, since version 1.3.20 Linux does actually wait.
> -(This still does not guarantee data integrity: modern disks have
> -large caches.)
> +writing is done.  However Linux waits for I/O completions,
> +and thus
> +.BR sync ()
> +or
> +.BR syncfs ()
> +provide the same guarantees as fsync called on every file in
> +the system or filesystem respectively.
> +.SH BUGS
> +Before version 1.3.20 Linux did not wait for I/O to complete
> +before returning.
>  .SH SEE ALSO
> -.BR bdflush (2),
>  .BR fdatasync (2),
>  .BR fsync (2),
>  .BR sync (1)
> --
> To unsubscribe from this list: send the line "unsubscribe linux-man" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> .
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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