On Fri 2021-06-11 23:59:52, Jia He wrote: > 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 change the behavior of '%pD' to print full path of that file. > > Things become more complicated when spec.precision and spec.field_width > is added in. string_truncate() is to handle the small space case for > '%pD' precision and field_width. > > [1] https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@xxxxxxxxxxxxxx/ > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Jia He <justin.he@xxxxxxx> > --- > Documentation/core-api/printk-formats.rst | 5 ++- > lib/vsprintf.c | 47 +++++++++++++++++++++-- > 2 files changed, 46 insertions(+), 6 deletions(-) > > diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst > index f063a384c7c8..95ba14dc529b 100644 > --- a/Documentation/core-api/printk-formats.rst > +++ b/Documentation/core-api/printk-formats.rst > @@ -408,12 +408,13 @@ dentry names > :: > > %pd{,2,3,4} > - %pD{,2,3,4} > + %pD > > For printing dentry name; if we race with :c:func:`d_move`, the name might > be a mix of old and new ones, but it won't oops. %pd dentry is a safer > equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n`` > -last components. %pD does the same thing for struct file. > +last components. %pD prints full file path together with mount-related > +parenthood. > > Passed by reference. > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index f0c35d9b65bf..317b65280252 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> > @@ -601,6 +602,20 @@ char *widen_string(char *buf, int n, char *end, struct printf_spec spec) > } > > /* Handle string from a well known address. */ This comment is for widen_string(). string_truncate() functionality is far from obvious. It would deserve it's own description, including description of each parammeter. Well, do we really need it? See below. > +static char *string_truncate(char *buf, char *end, const char *s, > + u32 full_len, struct printf_spec spec) > +{ > + int lim = 0; > + > + if (buf < end) { > + if (spec.precision >= 0) > + lim = strlen(s) - min_t(int, spec.precision, strlen(s)); > + > + return widen_string(buf + full_len, full_len, end - lim, spec); > + } > + > + return buf; > +} > static char *string_nocheck(char *buf, char *end, const char *s, > struct printf_spec spec) > { > @@ -920,13 +935,37 @@ 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); > + > + /* Minus 1 byte for '\0' */ > + dpath_len = end - buf - prepend_len - 1; > + > + reserved_size = max_t(int, dpath_len, spec.field_width); > + > + /* no filling space at all */ > + if (buf >= end || !buf) > + return buf + reserved_size; > + > + /* small space for long name */ > + if (buf < end && prepend_len < 0) > + return string_truncate(buf, end, p, dpath_len, spec); We need this only because we allowed to write the path behind spec.field_width. Do I get it right? > + > + /* space is enough */ > + return string_nocheck(buf, end, p, spec); > } It easy to get lost in all the computations, including the one in string_truncate(): dpath_len = end - buf - prepend_len - 1; reserved_size = max_t(int, dpath_len, spec.field_width); and lim = strlen(s) - min_t(int, spec.precision, strlen(s)); return widen_string(buf + full_len, full_len, end - lim, spec); Please, add comments explaining the meaning of the variables a bit. They should help to understand why it is done this way. I tried another approach below. The main trick is that max_len is limited by spec.field_width and spec.precision before calling d_path_unsave(): if (check_pointer(&buf, end, f, spec)) return buf; path = &f->f_path; if (check_pointer(&buf, end, path, spec)) return buf; max_len = end - buf; if (spec.field_width >= 0 && spec.field_width < max_len) max_len = spec.filed_width; if (spec.precision >= 0 && spec.precision < max_len) max_len = spec.precision; p = d_path_unsafe(path, buf, max_len, &prepend_len); /* * The path has been printed from the end of the buffer. * Process it like a normal string to handle "precission" * and "width" effects. In the "worst" case, the string * will stay as is. */ if (buf < end) { buf = string_nocheck(buf, end, p, spec); /* Return buf when output was limited or did fit in. */ if (spec.field_width >= 0 || spec.precision >= 0 || prepend_len >= 0) { return buf; } /* Otherwise, add what was missing. Ignore tail '\0' */ return buf - prepend_len - 1; } /* * Nothing has been written to the buffer. Just count the length. * I is fixed when field_with is defined. */ if (spec.field_width >= 0) return buf + spec.field_width; /* Otherwise, use the length of the path. */ dpath_len = max_len - prepend_len - 1; /* The path might still get limited by precision number. */ if (spec.precision >= 0 && spec.precision < dpath_len) return buf + spec.precision; return buf + dpath_len; Note that the above code is not even compile tested. There might be off by one mistakes. Also, it is possible that I missed something. Best Regards, Petr
