Re: [PATCH RFCv4 2/4] lib/vsprintf.c: make '%pD' print full path for file
From: Petr Mladek <pmladek@suse.com>
Date: 2021-06-17 14:09:57
Also in:
linux-fsdevel, lkml
On Tue 2021-06-15 23:49:50, Jia He wrote:
Previously, the specifier '%pD' is for printing dentry name of struct file. 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 change the behavior of '%pD' to print full path of that file. Precision is never going to be used with %p (or any of its kernel extensions) if -Wformat is turned on. . [1] https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@mail.gmail.com/ (local) Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jia He <redacted>
quoted hunk ↗ jump to hunk
--- a/lib/vsprintf.c +++ b/lib/vsprintf.c@@ -920,13 +921,41 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp } static noinline_for_stack -char *file_dentry_name(char *buf, char *end, const struct file *f, +char *file_d_path_name(char *buf, char *end, const struct file *f, struct printf_spec spec, const char *fmt) { + const struct path *path; + char *p; + int prepend_len, reserved_size, dpath_len; + if (check_pointer(&buf, end, f, spec)) return buf; - return dentry_name(buf, end, f->f_path.dentry, spec, fmt); + path = &f->f_path; + if (check_pointer(&buf, end, path, spec)) + return buf; + + p = d_path_unsafe(path, buf, end - buf, &prepend_len); + + /* Calculate the full d_path length, ignoring the tail '\0' */ + dpath_len = end - buf - prepend_len - 1; + + reserved_size = max_t(int, dpath_len, spec.field_width);
"reserved_size" is kind of confusing. "dpath_widen_len" or just "widen_len" look much more obvious. The below comments are not bad. But they still made me thing about it more than I wanted ;-) I wonder if it following is better:
+ /* case 1: no space at all, forward the buf with reserved size */ + if (buf >= end) + return buf + reserved_size;
/* Case 1: Already started past the buffer. Just forward @buf. */ if (buf >= end) return buf + widen_len;
+ + /* + * case 2: small scratch space for long d_path name. The space + * [buf,end] has been filled with truncated string. Hence use the + * full dpath_len for further string widening. + */ + if (prepend_len < 0) + return widen_string(buf + dpath_len, dpath_len, end, spec);
/* * Case 2: The entire remaining space of the buffer filled by * the truncated path. Still need to get moved right when * the filed width is greather than the full path length. */ if (prepend_len < 0) return widen_string(buf + dpath_len, dpath_len, end, spec);
+ /* case3: space is big enough */ + return string_nocheck(buf, end, p, spec);
/* * Case 3: The full path is printed at the end of the buffer. * Print it at the right location in the same buffer. */ return string_nocheck(buf, end, p, spec);
} #ifdef CONFIG_BLOCK static noinline_for_stack
In each case, I am happy that it was possible to simplify the logic. I got lost several times in the previous version. Best Regards, Petr