On 02/04/2015 12:51 PM, Michael Kerrisk (man-pages) wrote:
Hi Jan,
On 4 February 2015 at 09:48, Jan Chaloupka <jchaloup@xxxxxxxxxx> wrote:
Based on kernel commit [1], new flag f_flag is added to statfs struct.
Before kernel 2.6.36, glibc's statvfs.f_flags was computed be iterating
through all mounted points. This was inefficient and could cause a delay.
Since kernel 2.6.36, statfs struct has new field f_flag, which already
extracts mount options without iterating through mount point.
statfs.f_flag flags of glibc and kernel are the same (plus kernel adds
additional flag ST_VALID used only internally). So no matter what version
of kernel is used, flags does not change.
Flags used in statfs.f_flags can be enumerated from upstreams's
glibc/internal_statvfs.c, lines 155-173. Nine flags in sum:
ST_RDONLY = 1
ST_NOSUID = 2
ST_NODEV = 4
ST_NOEXEC = 8
ST_SYNCHRONOUS = 16
ST_MANDLOCK = 64
ST_NOATIME = 1024
ST_NODIRATIME = 2048
ST_RELATIME = 4096
This patch describes missing flag.
[1] https://github.com/torvalds/linux/commit/365b18189789bfa1acd9939e6312b8a4b4577b28
Thanks for the heads up. But this patch is a bit muddled, since it
mixes details about statfs(2) and statvfs(3).
Yes. As kernel copied all the flags, it is now duplicated. But you are
right it more suites for statvfs(2).
I've instead made some more detailed changes for the statfs(2) and statvfs(2) pages.
Thanks.
Thanks,
Michael
Signed-off-by: Jan Chaloupka <jchaloup@xxxxxxxxxx>
---
man2/statfs.2 | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/man2/statfs.2 b/man2/statfs.2
index 714bc7c..46cfa5f 100644
--- a/man2/statfs.2
+++ b/man2/statfs.2
@@ -65,7 +65,9 @@ struct statfs {
fsid_t f_fsid; /* filesystem id */
__SWORD_TYPE f_namelen; /* maximum length of filenames */
__SWORD_TYPE f_frsize; /* fragment size (since Linux 2.6) */
- __SWORD_TYPE f_spare[5];
+ __SWORD_TYPE f_flags; /* mount flags of filesystem
+ (since Linux 2.6.36) */
+ __SWORD_TYPE f_spare[4];
};
Filesystem types:
@@ -146,6 +148,30 @@ Most of these MAGIC constants are defined in
.IR /usr/include/linux/magic.h ,
and some are hardcoded in kernel sources.
.PP
+Mount flags of
+.I f_flags
+field are extracted from an option string of a mount point defined in
+.BR mount (8).
+The field can be combination of the following flags
+(corresponding mount options are in the right column):
+.in
+.nf
+
+ ST_RDONLY ro
+ ST_NOSUID nosuid
+ ST_NOEXEC noexec
+ ST_NODEV nodev
+ ST_SYNCHRONOUS sync
+ ST_MANDLOCK mand
+ ST_NOATIME noatime
+ ST_NODIRATIME nodiratime
+ ST_RELATIME relatime
+
+.fi
+.in
+For kernel less than 2.6.36 option flags are extracted by iterating
+through individual mount points which can be inefficient and cause delay.
+.PP
Nobody knows what
.I f_fsid
is supposed to contain (but see below).
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