On 20.05.2014 09:36, Michael Kerrisk (man-pages) wrote:
Hi Heinrich,
On 05/19/2014 08:58 PM, Heinrich Schuchardt wrote:
Hello Michael,
the proposed new description of FAN_EVENT_NEXT is correct.
Thanks for checking. I've added a Reviewed-by for you.
Should FAN_EVENT_METADATA_LEN also be put into the section with macros?
.B FAN_EVENT_METADATA_LEN
This macro returns the size of structure
.I fanotify_event_metadata
in bytes.
This is the minimum size (and currently the only size) of any event
metadata.
I'm inclined not to, but I might be wrong. Is there a reason that
user-space might use it?
FAN_EVENT_METADATA_LEN is the minimum size of a buffer used to read
fanotify events. Of cause the user may use sizeof to calculate it
himself. Anyway there is already some mentioning of
FAN_EVENT_METADATA_LEN in fanotify.7.
You remarked inotify read buffers should be 4 byte aligned on some CPUs.
Shouldn't the same hold true for fanotify?
Best regards
Heinrich
Cheers,
Michael
On 19.05.2014 07:20, Michael Kerrisk (man-pages) wrote:
Hi Heinrich,
I realized that the description of FAN_EVENT_NEXT() is not quite correct.
It does not update 'meta', but instead returns a pointer to the next
structure. I tried also to add a bit more detail to the description.
Does the following patch look okay to you?
Cheers,
Michael
--- a/man7/fanotify.7
+++ b/man7/fanotify.7
@@ -309,13 +309,24 @@ against the length of the metadata structure and the
field of the first metadata structure in the buffer.
.TP
.B FAN_EVENT_NEXT(meta, len)
-This macro sets the pointer
-.I meta
-to the next metadata structure using the length indicated in the
+This macro uses the length indicated in the
.I event_len
-field of the metadata structure and reduces the remaining length of the
-buffer
-.IR len .
+field of the metadata structure pointed to by
+.IR meta
+to calculate the address of the next metadata structure that follows
+.IR meta .
+.I len
+is the number of bytes of metadata that currently remain in the buffer.
+The macro returns a pointer to the next metadata structure that follows
+.IR meta ,
+and reduces
+.I len
+by the number of bytes in the the metadata structure that
+has been skipped over (i.e., it subtracts
+.IR meta\->event_len
+from
+.IR len ).
+.\"
.SS Monitoring an fanotify file descriptor for events
When an fanotify event occurs, the fanotify file descriptor indicates as
readable when passed to
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