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Add more detail about wrapper functions 

Add a few more details about work generally done by wrapper
functions.  Note that syscall(2) performs the same steps.
This commit is contained in:
Michael Kerrisk 2008-09-24 16:10:00 +02:00
parent c892873d1a
commit c8bd05f909
2 changed files with 20 additions and 1 deletions
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@ -32,3 +32,7 @@ Global changes
Changes to individual pages
---------------------------
syscalls.2
mtk
Add a few more details about work generally done by wrapper
functions. Note that syscall(2) performs the same steps.

17
man2/syscalls.2
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@ -46,7 +46,22 @@ For example, glibc contains a function
which invokes the underlying "truncate" system call.
Often the glibc wrapper function is quite thin, doing little work
before invoking the system call.
other than copying arguments to the right registers
before invoking the system call,
and then setting
.I errno
appropriately after the system call has returned.
(These are the same steps that are performed by
.BR syscall (2),
which can be used to invoke system calls
for which no wrapper function is provided.)
Note: system calls indicate a failure by returning a negative error
number to the caller;
when this happens,
the wrapper function negates the returned error number
(to make it positive), copies it to
.IR errno ,
and returns \-1 to the caller of the wrapper.
Sometimes, however, the wrapper function does some extra work
before invoking the system call.