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Diffstat (limited to 'Documentation/filesystems/seq_file.txt')
| -rw-r--r-- | Documentation/filesystems/seq_file.txt | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt index cc6cdb95b73..b843743aa0b 100644 --- a/Documentation/filesystems/seq_file.txt +++ b/Documentation/filesystems/seq_file.txt @@ -92,7 +92,7 @@ implementations; in most cases the start() function should check for a "past end of file" condition and return NULL if need be. For more complicated applications, the private field of the seq_file -structure can be used. There is also a special value whch can be returned +structure can be used. There is also a special value which can be returned by the start() function called SEQ_START_TOKEN; it can be used if you wish to instruct your show() function (described below) to print a header at the top of the output. SEQ_START_TOKEN should only be used if the offset is @@ -122,8 +122,7 @@ stop() is the place to free it. } Finally, the show() function should format the object currently pointed to -by the iterator for output. It should return zero, or an error code if -something goes wrong. The example module's show() function is: +by the iterator for output. The example module's show() function is: static int ct_seq_show(struct seq_file *s, void *v) { @@ -132,6 +131,12 @@ something goes wrong. The example module's show() function is: return 0; } +If all is well, the show() function should return zero. A negative error +code in the usual manner indicates that something went wrong; it will be +passed back to user space. This function can also return SEQ_SKIP, which +causes the current item to be skipped; if the show() function has already +generated output before returning SEQ_SKIP, that output will be dropped. + We will look at seq_printf() in a moment. But first, the definition of the seq_file iterator is finished by creating a seq_operations structure with the four functions we have just defined: @@ -146,7 +151,7 @@ the four functions we have just defined: This structure will be needed to tie our iterator to the /proc file in a little bit. -It's worth noting that the interator value returned by start() and +It's worth noting that the iterator value returned by start() and manipulated by the other functions is considered to be completely opaque by the seq_file code. It can thus be anything that is useful in stepping through the data to be output. Counters can be useful, but it could also be @@ -182,12 +187,18 @@ The first two output a single character and a string, just like one would expect. seq_escape() is like seq_puts(), except that any character in s which is in the string esc will be represented in octal form in the output. -There is also a function for printing filenames: +There is also a pair of functions for printing filenames: int seq_path(struct seq_file *m, struct path *path, char *esc); + int seq_path_root(struct seq_file *m, struct path *path, + struct path *root, char *esc) Here, path indicates the file of interest, and esc is a set of characters -which should be escaped in the output. +which should be escaped in the output. A call to seq_path() will output +the path relative to the current process's filesystem root. If a different +root is desired, it can be used with seq_path_root(). Note that, if it +turns out that path cannot be reached from root, the value of root will be +changed in seq_file_root() to a root which *does* work. Making it all work @@ -262,7 +273,7 @@ routines useful: These helpers will interpret pos as a position within the list and iterate accordingly. Your start() and next() functions need only invoke the -seq_list_* helpers with a pointer to the appropriate list_head structure. +seq_list_* helpers with a pointer to the appropriate list_head structure. The extra-simple version |