Re: [PATCH RFC 2/3] lib/vsprintf.c: make %pD print full path for file
From: Petr Mladek <pmladek@suse.com>
Date: 2021-05-10 13:38:54
Also in:
linux-fsdevel, linux-s390, lkml
On Sat 2021-05-08 20:25:29, Jia He wrote:
quoted hunk ↗ jump to hunk
We have '%pD' for printing a filename. It may not be perfect (by default it only prints one component.) As suggested by Linus at [1]: A dentry has a parent, but at the same time, a dentry really does inherently have "one name" (and given just the dentry pointers, you can't show mount-related parenthood, so in many ways the "show just one name" makes sense for "%pd" in ways it doesn't necessarily for "%pD"). But while a dentry arguably has that "one primary component", a _file_ is certainly not exclusively about that last component. Hence "file_dentry_name()" simply shouldn't use "dentry_name()" at all. Despite that shared code origin, and despite that similar letter choice (lower-vs-upper case), a dentry and a file really are very different from a name standpoint.diff --git a/lib/vsprintf.c b/lib/vsprintf.c index f0c35d9b65bf..8220ab1411c5 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c@@ -27,6 +27,7 @@ #include <linux/string.h> #include <linux/ctype.h> #include <linux/kernel.h> +#include <linux/dcache.h> #include <linux/kallsyms.h> #include <linux/math64.h> #include <linux/uaccess.h>@@ -923,10 +924,17 @@ static noinline_for_stack char *file_dentry_name(char *buf, char *end, const struct file *f, struct printf_spec spec, const char *fmt) { + const struct path *path = &f->f_path;
This dereferences @f before it is checked by check_pointer().
+ char *p; + char tmp[128]; + if (check_pointer(&buf, end, f, spec)) return buf; - return dentry_name(buf, end, f->f_path.dentry, spec, fmt); + p = d_path_fast(path, (char *)tmp, 128); + buf = string(buf, end, p, spec);
Is 128 a limit of the path or just a compromise, please?
d_path_fast() limits the size of the buffer so we could use @buf
directly. We basically need to imitate what string_nocheck() does:
+ the length is limited by min(spec.precision, end-buf);
+ the string need to get shifted by widen_string()
We already do similar thing in dentry_name(). It might look like:
char *file_dentry_name(char *buf, char *end, const struct file *f,
struct printf_spec spec, const char *fmt)
{
const struct path *path;
int lim, len;
char *p;
if (check_pointer(&buf, end, f, spec))
return buf;
path = &f->f_path;
if (check_pointer(&buf, end, path, spec))
return buf;
lim = min(spec.precision, end - buf);
p = d_path_fast(path, buf, lim);
if (IS_ERR(p))
return err_ptr(buf, end, p, spec);
len = strlen(buf);
return widen_string(buf + len, len, end, spec);
}
Note that the code is _not_ even compile tested. It might include
some ugly mistake.
quoted hunk ↗ jump to hunk
+ + return buf; } #ifdef CONFIG_BLOCK static noinline_for_stack@@ -2296,7 +2304,7 @@ early_param("no_hash_pointers", no_hash_pointers_enable); * - 'a[pd]' For address types [p] phys_addr_t, [d] dma_addr_t and derivatives * (default assumed to be phys_addr_t, passed by reference) * - 'd[234]' For a dentry name (optionally 2-4 last components) - * - 'D[234]' Same as 'd' but for a struct file + * - 'D' Same as 'd' but for a struct file
It is not really the same. We should make it clear that it prints the full path: + * - 'D' Same as 'd' but for a struct file; prints full path with + the mount-related parenthood
* - 'g' For block_device name (gendisk + partition number) * - 't[RT][dt][r]' For time and date as represented by: * R struct rtc_time -- 2.17.1
Best Regards, Petr