I followed the implementation of the du command (second half)
Introduction
This is a continuation of Last time. We will continue to follow the implementation of the du command.
review
I will repost the du_files () I saw last time.
python
/* Recursively print the sizes of the directories (and, if selected, files)
named in FILES, the last entry of which is NULL.
BIT_FLAGS controls how fts works.
Return true if successful. */
static bool
du_files (char **files, int bit_flags)
{
bool ok = true;
if (*files)
{
FTS *fts = xfts_open (files, bit_flags, NULL); //(1)
while (1)
{
FTSENT *ent;
ent = fts_read (fts); //(2)
if (ent == NULL)
{
if (errno != 0)
{
error (0, errno, _("fts_read failed"));
ok = false;
}
break;
}
FTS_CROSS_CHECK (fts);
ok &= process_file (fts, ent); //(3)
}
if (fts_close (fts) != 0)
{
error (0, errno, _("fts_close failed"));
ok = false;
}
}
return ok;
}
The processing performed here is the following three.
(1). Get the FTS structure from the file name with xfts_open ().
(2). Get the FTSENT structure from the FTS structure with fts_read (). --- Until last time
(3). Call process_file () and return to (2).
The figure is as follows.
This time, we will look at process_file () in (3).
process_file()
python
static bool
process_file (FTS *fts, FTSENT *ent)
{
bool ok = true;
struct duinfo dui;
struct duinfo dui_to_print;
size_t level;
static size_t prev_level;
static size_t n_alloc;
static struct dulevel *dulvl;
const char *file = ent->fts_path;
const struct stat *sb = ent->fts_statp;
//Continue
Let's look at the variables.
-
dui: Current directory information. The size field has the total file size under the directory. -
dui_to_print: Directory information for display. Information displayed on the screen when the du command is executed. -
level: The depth of the current file hierarchy. -
prev_level: The depth of the previous file hierarchy. -
n_alloc: A parameter used to allocatedulvl. Set to a value greater than the depth of the file hierarchy. -
dulvl: An array with directory information. The depth of the file hierarchy corresponds to the index of the array. For example, the information in the directory at depth 2 corresponds to dulvl [2]. The fields of the dulevel structure are: -
struct duinfo ent: Directory information excluding subdirectories. -
struct duinfo subdir: Directory information for subdirectories. -
The
sizefield of ʻentcontains the file size under the directory. However, the file size under the subdirectory is excluded. On the other hand, thesizefield ofsubdircontains the file size under the subdirectory. In other words, the sum ofsizeof ʻentandsubdirgives the file size including the subdirectories under the directory. -
file: The root path of the file. -
sb: A pointer to a stat structure. Get the file size from here.
duinfo_set()
Then call duinfo_set ().
python
duinfo_set (&dui,
(apparent_size
? MAX (0, sb->st_size)
: (uintmax_t) ST_NBLOCKS (*sb) * ST_NBLOCKSIZE),
(time_type == time_mtime ? get_stat_mtime (sb)
: time_type == time_atime ? get_stat_atime (sb)
: get_stat_ctime (sb)));
python
static inline void
duinfo_set (struct duinfo *a, uintmax_t size, struct timespec tmax)
{
a->size = size;
a->inodes = 1;
a->tmax = tmax;
}
duinfo_set () is a function that sets the file size and time stamp in the first argument dui.
ʻApparent_size is a flag that outputs the actual file size, not the disk usage. The disk usage of a file is the file size rounded up to the file system block size. For example, if the block size is 4Kbyte and the file size is 8.5Kbyte, the disk usage will be 12Kbyte. The du command displays disk usage by default. When ʻapparent_size is true, the actual file size is passed to the argument ofduinfo_set (), and when false, the block usage is passed.
Add file size
The file size has been set in dui byduinfo_set ().
See the next process.
python
level = ent->fts_level;
dui_to_print = dui;
Enter the depth of the file hierarchy in level. Also set dui_to_print.
The next step is to add the dui file size to the directory size.
The processing is divided into the following three patterns.
- When you are in the same file hierarchy as you followed
- When going down the file hierarchy and increasing in depth
- When you go up the file hierarchy and the depth decreases
1. When you are in the same file hierarchy as you followed
python
prev_level = level;
if (! (opt_separate_dirs && IS_DIR_TYPE (info)))
duinfo_add (&dulvl[level].ent, &dui);
duinfo_add (&tot_dui, &dui);
First, add the file size of dui to duvlv [level] .ent. dulvl [level] is a structure that handles directory information at depth level. Here, the total file size of the same hierarchy is calculated. Note that ʻopt_separate_dirs is an option that does not include the size of the subdirectory, and ʻIS_DIR_TYPE (ent-> fts_info) is true if the file you are looking at is a directory. That is, if you do not include subdirectories, the directory size will not be added.
Next, add the file size to tot_dui as well. tot_dui is the sum of all file sizes.
2. When going down the file hierarchy and increasing in depth
python
size_t i;
for (i = prev_level + 1; i <= level; i++)
{
duinfo_init (&dulvl[i].ent);
duinfo_init (&dulvl[i].subdir);
}
prev_level = level;
if (! (opt_separate_dirs && IS_DIR_TYPE (info)))
duinfo_add (&dulvl[level].ent, &dui);
duinfo_add (&tot_dui, &dui);
When you go down the file hierarchy, you will be in that directory for the first time, so initialize dulvl [i] with duinfo_init (). The rest of the process is the same as before.
3. When you go up the file hierarchy and the depth decreases
python
duinfo_add (&dui_to_print, &dulvl[prev_level].ent);
if (!opt_separate_dirs)
duinfo_add (&dui_to_print, &dulvl[prev_level].subdir);
duinfo_add (&dulvl[level].subdir, &dulvl[prev_level].ent);
duinfo_add (&dulvl[level].subdir, &dulvl[prev_level].subdir);
prev_level = level;
if (! (opt_separate_dirs && IS_DIR_TYPE (ent->fts_info)))
duinfo_add (&dulvl[level].ent, &dui);
duinfo_add (&tot_dui, &dui);
When you go up the file hierarchy, the previous location is the current subdirectory. So, add the capacity of the previous directory to dui_to_print and dulvl [level] .subdir.
Finally, if the file you are looking at is a directory, it will display the directory capacity.
python
if ((IS_DIR_TYPE (ent->fts_info) && level <= max_depth)
|| ((opt_all && level <= max_depth) || level == 0))
print_size (&dui_to_print, file);
in conclusion
This is the first time I have read the source code of a command, but it is also recommended for beginners because the code is not long and the operating principle is simple. Also, it is fun to read while anticipating the operating principle of the command.
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