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@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 | 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> #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 */ + if (buf >= end) + return buf + reserved_size; + + /* + * 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); + + /* case3: space is big enough */ + 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
