Date: Mon, 18 Feb 2008 11:45:11 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: "Daniel O'Connor" <doconnor@gsoft.com.au> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-current@freebsd.org, Giorgos Keramidas <keramida@freebsd.org> Subject: Re: [src] cvs commit: src/include unistd.h src/lib/libc/sys readlink.2 src/sys/compat/freebsd32 syscalls.master src/sys/kern syscalls.master vfs_syscalls.c src/sys/sys syscallsubr.h Message-ID: <86pruu7dc8.fsf@ds4.des.no> In-Reply-To: <200802181513.42681.doconnor@gsoft.com.au> (Daniel O'Connor's message of "Mon\, 18 Feb 2008 15\:13\:35 %2B1030") References: <200802122009.m1CK94Y8026959@repoman.freebsd.org> <200802181004.21379.doconnor@gsoft.com.au> <20080218040625.GA8141@kobe.laptop> <200802181513.42681.doconnor@gsoft.com.au>
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"Daniel O'Connor" <doconnor@gsoft.com.au> writes: > Giorgos Keramidas <keramida@freebsd.org> writes: > > Specifying stdout may be a bit tricky, since the traced application > > may be using the same stream to print output. The same is possible > > with stderr, but may be a tiny bit less likely. > I didn't realise that the file descriptor used to write tracing data > out was 'owned' by the process being traced, I always thought ktrace > did. ktrace does absolutely nothing other than enable tracing and exec the application. The 'k' in "ktrace" means "kernel". > I did have a look at the source and the file opening etc is handled by > the kernel but I am not sure who 'owns' that file descriptor. There is no file descriptor. There is a vnode in the kernel which is not listed in the traced process's file table. This is the whole point of ktrace: it is undetectable by the traced process. > I guess it couldn't be moved to ktrace without rearchitecting how > ktracing works so the ktrace process sticks around writing stuff out > to disk. ...which would make it just as useless as truss, since it would (among other things) change the way job control works for the traced process. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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