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Message-ID: <CAHp75Vdu=_qgOeQJsR=60aJ-2y3RgurTO=gqKgxmcVZKq1eUYw@mail.gmail.com>
Date: Tue, 15 Jun 2021 23:44:51 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Jia He <justin.he@....com>
Cc: Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Jonathan Corbet <corbet@....net>,
Alexander Viro <viro@...iv.linux.org.uk>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Eric Biggers <ebiggers@...gle.com>,
"Ahmed S. Darwish" <a.darwish@...utronix.de>,
Linux Documentation List <linux-doc@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH RFCv4 2/4] lib/vsprintf.c: make '%pD' print full path for file
On Tue, Jun 15, 2021 at 6:54 PM Jia He <justin.he@....com> 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.
print the full
>
> 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/
Put it as a Link: tag?
>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Jia He <justin.he@....com>
> ---
> Documentation/core-api/printk-formats.rst | 5 +--
> lib/vsprintf.c | 37 ++++++++++++++++++++---
> 2 files changed, 36 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..9d3166332726 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>
I know that this is an arbitrary order, but can you keep it after ctype.h?
> #include <linux/kallsyms.h>
> #include <linux/math64.h>
> #include <linux/uaccess.h>
> @@ -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);
> +
> + /* case 1: no space at all, forward the buf with reserved size */
Case 1:
> + if (buf >= end)
> + return buf + reserved_size;
> +
> + /*
> + * case 2: small scratch space for long d_path name. The space
Case 2:
> + * [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);
> +
> + /* case3: space is big enough */
Case 3:
> + return string_nocheck(buf, end, p, spec);
> }
> #ifdef CONFIG_BLOCK
> static noinline_for_stack
> @@ -2296,7 +2325,7 @@ 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' For full path name of a struct file
> * - 'g' For block_device name (gendisk + partition number)
> * - 't[RT][dt][r]' For time and date as represented by:
> * R struct rtc_time
> @@ -2395,7 +2424,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> case 'C':
> return clock(buf, end, ptr, spec, fmt);
> case 'D':
> - return file_dentry_name(buf, end, ptr, spec, fmt);
> + return file_d_path_name(buf, end, ptr, spec, fmt);
> #ifdef CONFIG_BLOCK
> case 'g':
> return bdev_name(buf, end, ptr, spec, fmt);
> --
> 2.17.1
>
--
With Best Regards,
Andy Shevchenko
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