Messages in this thread | | | Date | Mon, 9 Dec 2013 21:42:23 +0800 | Subject | Re: [PATCH] xen/debugfs: Check debugfs initialization before using it | From | Ethan Zhao <> |
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Greg, I am the man who built a Xen dom0, but couldn't see debugfs directory and files as expected. there is no warning or tip for me to enable the CONFIG_DEBUG_FS=y in .config , it cost me minutes to figure out what's the matter. and I know should check defugfs config and initialization as zswap_debugfs, tracer_debugfs ,rproc_debugfs did. Is it useless ? if it could save me just 1 minute next time ?
Thanks, Ethan
On Mon, Dec 9, 2013 at 7:17 PM, Greg KH <gregkh@linuxfoundation.org> wrote: > On Mon, Dec 09, 2013 at 05:57:22PM +0800, Ethan Zhao wrote: >> On Mon, Dec 9, 2013 at 4:55 PM, Greg KH <gregkh@linuxfoundation.org> wrote: >> > On Mon, Dec 09, 2013 at 04:44:05PM +0800, Ethan Zhao wrote: >> >> On Mon, Dec 9, 2013 at 4:25 PM, Greg KH <gregkh@linuxfoundation.org> wrote: >> >> > On Mon, Dec 09, 2013 at 09:43:16AM +0800, Ethan Zhao wrote: >> >> >> On Sun, Dec 8, 2013 at 10:01 PM, Greg KH <gregkh@linuxfoundation.org> wrote: >> >> >> > On Sun, Dec 08, 2013 at 07:31:02PM +0800, ethan.zhao wrote: >> >> >> >> Should check debugfs initialization with debugfs_initialized() before using it, >> >> >> >> Because if it isn't initialized, the return value of fake debugfs_create_dir() etc >> >> >> >> functions would be ERR_PTR(-ENODEV), checking with NULL will not work. >> >> >> > >> >> >> > So? It should "just work" without this check, right? What happens if >> >> >> > your patch isn't applied and debugfs isn't enabled? >> >> >> >> >> >> If debugfs isn't configured, debugfs_initialized() and other >> >> >> functions are defined as following, >> >> >> >> >> >> static inline bool debugfs_initialized(void) >> >> >> { >> >> >> return false; >> >> >> } >> >> >> >> >> >> static inline struct dentry *debugfs_create_file(const char *name, umode_t mode, >> >> >> struct dentry *parent, void *data, >> >> >> const struct file_operations *fops) >> >> >> { >> >> >> return ERR_PTR(-ENODEV); >> >> >> } >> >> >> >> >> >> static inline struct dentry *debugfs_create_dir(const char *name, >> >> >> struct dentry *parent) >> >> >> { >> >> >> return ERR_PTR(-ENODEV); >> >> >> } >> >> >> >> >> >> And the checking code in xen\debugfs.c xen_init_debugfs() will not >> >> >> work, the return value is not NULL. >> >> >> d_xen_debug = debugfs_create_dir("xen", NULL); >> >> >> >> >> >> if (!d_xen_debug) >> >> >> pr_warning("Could not create 'xen' debugfs directory\n"); >> >> > >> >> > Which is just fine, what is wrong with this? >> >> >> >> If we no check with debugfs_initialized(), the above code should be >> >> if (!d_xen_debug || IS_ERR (d_xen_debug)) >> >> pr_warning("Could not create 'xen' debugfs directory\n"); >> > >> > No, you don't want to print out that message if debugfs is not enabled. >> > >> > You really don't want to print anything out, as what can a user do about >> > this? >> > >> Yep, should output a warning about "Debugfs is not configured and enabled" > > No, not at all, it's not an issue you need to warn about because it was > explicitly told to be that way by the person who built that kernel. > > It's not an error, please don't treat it as such. > > greg k-h
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