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FS.md

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# FS
## **Overview**
Provides functions for file system, include file operations, directory operations and so on.
**Since:**
1.0
**Version:**
1.0
## **Summary**
## Files

File Name	Description
dirent.h	Provides functions and structures used for performing file system operations, including file read/write, directory traversal, and file system mounting.
fcntl.h	Declares structures and functions used for file and directory operations such as opening a file, creating a file, and allocating space.
ftw.h	Provides functions and structures related to file tree traversal.
glob.h	Provides functions and structures used to find path names matching a pattern and release the memory that was applied for during the search.
libgen.h	Provides functions related to file management, for example, obtaining directory and file names.
ioctl.h	Manipulates a device.
mount.h	Provides functions for mounting and unmounting a file system.
stat.h	Provides functions for file and directory operations.
statfs.h	Provides a function to obtain information about a file system.
statvfs.h	Provides a function and structure related to file system information operation, for example, viewing file system information.
utime.h	Provides the function and structure used for setting file access time and modification time.

## Data Structures

Data Structure Name	Description
dirent	Defines the content of the directory.
FTW	Defines the file tree walker (FTW).
glob_t	Defines the search information.
stat	Defines the file information structure.
statvfs	Describes file system information.
utimbuf	Defines the file access time and modification time.

## Macros

Macro Name and Value	Description
O_ACCMODE (03\|O_SEARCH)	Access mode.
O_RDONLY 00	Read-only.
O_WRONLY 01	Write-only.
O_RDWR 02	Read and write.
fallocate64 fallocate	Pre-allocates space to a file. See fallocate.
FTW_F 1	Regular file.
FTW_D 2	Directory.
FTW_DNR 3	Unreadable directory. Its subdirectories will not be traversed.
FTW_NS 4	The data of the stat structure cannot be obtained. The possible cause is that the permission is incorrect.
FTW_SL 5	Symbolic link.
FTW_DP 6
FTW_SLN 7	Symbolic link that names a non-existent file.
FTW_PHYS 1	Symbolic links that are not traversed. If not set, symbolic links are traversed by default.
FTW_MOUNT 2	Stay within the same file system.
FTW_CHDIR 4	chdir is called to go to the directory before reading the directory.
FTW_DEPTH 8	All subdirectories will be traversed before the directory itself.
GLOB_ERR 0x01	Return upon a read error.
GLOB_MARK 0x02	Append a slash (/) to each path, which corresponds to a directory.
GLOB_NOSORT 0x04	Do not sort the returned path names.
GLOB_DOOFFS 0x08	In the pglob parameter of the glob() function, reserve a string that has a length of pglob->gl_offs and ends with \0 at the beginning of the string list in pglob->pathv. That is, the newly matched string is appended to a position where the distance from the beginning of pglob->pathv is the length of pglob->gl_offs.
GLOB_NOCHECK 0x10	If no pattern matches, return the original pattern.
GLOB_APPEND 0x20	Append the results of this call to the results returned by a previous call to glob().
GLOB_NOESCAPE 0x40	Do not use a backslash () as an escape character.
GLOB_PERIOD 0x80	Allow a leading period to be matched by metacharacters.
GLOB_TILDE 0x1000	Carry out tilde expansion. If a tilde (~) is the only character in the pattern, or an initial tilde is followed immediately by a slash (/), then the home directory of the caller is substituted for the tilde.
GLOB_TILDE_CHECK 0x4000	Similar to GLOB_TILDE. The difference is that if the username is invalid, or the home directory cannot be determined, glob() returns GLOB_NOMATCH to indicate an error.
GLOB_NOSPACE 1	Memory insufficient.
GLOB_ABORTED 2	Read error.
GLOB_NOMATCH 3	No matching item is found.
GLOB_NOSYS 4	The function is not supported.

## Typedefs

Typedef Name	Description
DIR	typedef struct __dirstream Opens the handle of the folder directory.

## Functions

Function Name	Description
closedir (DIR *dirp)	int Closes a specified directory.
opendir (const char *dirname)	DIR * Opens a specified directory.
readdir (DIR *dirp)	struct dirent * Reads a specified directory.
readdir_r (DIR __restrict dirp, struct dirent __restrict entry, struct dirent **__restrict result)	int Reads a specified directory (thread-safe version).
rewinddir (DIR *dirp)	void Resets a directory stream read position.
alphasort (const struct dirent a, const struct dirent b)	int Sorts the directory entries in alphabetical order.
scandir (const char dir, struct dirent *namelist, int(sel)(const struct dirent ), int(compar)(const struct dirent , const struct dirent ))	int Scans directory to find the target entries.
seekdir (DIR *dirp, long offset)	void Sets the position of the next readdir call in the directory stream.
telldir (DIR *dirp)	long Obtains the current position in the specified directory stream.
creat (const char *path, mode_t mode)	int Creates a file or rewrites an existing file.
open (const char *path, int oflags,...)	int Opens a file.
fallocate (int fd, int mode, off_t offset, off_t len)	int Pre-allocates space to a file.
fcntl (int fd, int cmd,...)	int Manipulates a specified file descriptor.
ftw (const char path, int(fn)(const char file, const struct stat sb, int flag), int depth)	int Traverses a file tree.
nftw (const char path, int(fn)(const char file, const struct stat sb, int flag, struct FTW *s), int fd_limit, int flags)	int Traverses a file tree.
glob (const char __restrict pattern, int flags, int(errfunc)(const char , int), glob_t __restrict pglob)	int Searches for path names that meet a specified pattern.
globfree (glob_t *pglob)	void Frees allocated memory from a call to glob().
dirname (char *path)	char * Obtains a directory name in a specified path.
basename (char *path)	char * Obtains a file name (excluding the directory) in a specified path.
ioctl (int fd, int cmd,...)	int Manipulates a device.
mount (const char source, const char target, const char filesystemtype, unsigned long mountflags, const void data)	int Mounts a file system.
umount (const char *target)	int Unmounts a file system.
umount2 (const char *target, int flags)	int Unmounts a file system.
stat (const char __restrict path, struct stat __restrict buf)	int Obtains file information.
fstat (int fd, struct stat *buf)	int Obtains file status information.
lstat (const char __restrict path, struct stat __restrict buf)	int Obtains file information.
mkdir (const char *pathname, mode_t mode)	int Creates a directory.
mkfifo (const char *name, mode_t mode)	int Creates a named pipe to implement inter-process communication.
mkdirat (int fd, const char *pathname, mode_t mode)	int Creates a directory.
chmod (const char *pathname, mode_t mode)	int Modifies permissions for a file.
umask (mode_t mode)	mode_t Sets umask for a process.
statfs (const char path, struct statfs buf)	int Obtains file system information of a file in a specified path.
statvfs (const char __restrict path, struct statvfs __restrict buf)	int Obtains the file system information.
utime (const char filename, const struct utimbuf times)	int Sets the access time and modification time of a file.

## **Details**
## **Macro Definition Documentation**
## FTW\_DP
```
#define FTW_DP 6
```
**Description:**
@briefDirectory. All subdirectories in this directory have been traversed.
## **Function Documentation**
## alphasort\(\)
```
int alphasort (const struct [dirent](dirent.md) ** a, const struct [dirent](dirent.md) ** b )
```
**Description:**
Sorts the directory entries in alphabetical order.
This function is used to sort the two directory entries passed through the input parameters in alphabetical order. Generally, these parameters are passed in [scandir](FS.md#gaca6df630e382cf13bac90ed6e5c4141c) as its last parameter.
**Parameters:**

Name	Description
a	Indicates the pointer to directory entry a.
a	Indicates the pointer to directory entry b.

**Returns:**
Returns an integer greater than, equal to, or less than **0**, respectively, based on whether the name of the directory entry to which **a** points is lexically greater than, equal to, or less than the directory.
## basename\(\)
```
char* basename (char * path)
```
**Description:**
Obtains a file name \(excluding the directory\) in a specified path.
**Parameters:**

Name	Description
path	Indicates the pointer to the path.

**Returns:**
Returns the file name if the operation is successful; returns **NULL** otherwise.
## chmod\(\)
```
int chmod (const char * pathname, mode_t mode )
```
**Description:**
Modifies permissions for a file.
**Parameters:**

Name	Description
pathname	Indicates the pointer to the path of the file.
mode	Indicates the new file permission.

**Attention:**
This function can be used only in the JFFS2 file system.
**Returns:**
Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	The pathname is a null pointer or an empty string.
EACCES	The permission bit of the file mode does not allow the requested access, or the search permission is denied on the path prefix directory.
EFAULT	Incorrect IP address.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOENT	The directory component in the path name does not exist.
ENOMEM	Insufficient memory.
ENOTDIR	A component of the path prefix is the name of an existing file. The file is neither a directory nor a symbolic link of a directory.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EROFS	The physical drive is write-protected.
EEXIST	The file or directory already exists.
ENOSYS	The function is not supported.

## closedir\(\)
```
int closedir ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) * dirp)
```
**Description:**
Closes a specified directory.
**Parameters:**

Name	Description
dirp	Indicates the pointer to the structure representing the directory to close.

**Returns:**
Returns **0** if the directory is successfully closed; returns **-1** and sets **errno** to the following value otherwise.

errno	Description
EBADF	dirp is not a valid opened directory stream.

## creat\(\)
```
int creat (const char * path, mode_t mode )
```
**Description:**
Creates a file or rewrites an existing file.
**Parameters:**

Name	Description
path	Indicates the pointer to the name of the file to create or rewrite.
mode	Indicates permissions on the file.

**Returns:**
Returns **0** if the file is created or rewritten successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	path points to an invalid path.
ENAMETOOLONG	The length of path is greater than the value of NAME_MAX.
ENXIO	Invalid inode or the inode is not a mount point.
EMFILE	All file descriptors that can be used by the process are opened.
EPERM	The file structure corresponding to the file descriptor cannot be obtained.
EACCES	Access denied by the permission bit of file mode
ENOMEM	The memory is insufficient.
ENODEV	The device does not exist.
EEXIST	O_CREAT and O_EXCL are set.
EIO	A hardware error occurs at the low-level disk I/O layer. As a result, the physical drive cannot work.
ENFILE	The number of opened files in the system has reached the maximum.
ENOTDIR	A component of the path prefix is the name of an existing file and is not a directory.
EBUSY	The operation is rejected according to the file sharing policy.
ENOTEMPTY	The directory is not empty.
ELOOP	Too many symbolic links are encountered.
EFAULT	The IP address is incorrect.

## dirname\(\)
```
char* dirname (char * path)
```
**Description:**
Obtains a directory name in a specified path.
**Parameters:**

Name	Description
path	Indicates the pointer to the path.

**Returns:**
Returns the directory name if the operation is successful; returns **NULL** otherwise.
## fallocate\(\)
```
int fallocate (int fd, int mode, off_t offset, off_t len )
```
**Description:**
Pre-allocates space to a file.
**Parameters:**

Name	Description
fd	Indicates the file descriptor.
mode	Indicates the operation mode. Only FALLOC_FL_KEEP_SIZE is supported.
offset	Indicates the offset of the file to allocate.
len	Indicates the size of the disk space to be allocated to the file.

**Attention:**
This function can be used only in the FAT file system.
**Returns:**
Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	The value of len or offset is less than 0 or greater than that of INT_MAX, or the value of mode is not FALLOC_FL_KEEP_SIZE.
EBADF	fd is not a valid file descriptor, or the basic file system does not support this operation.
EAGAIN	The file list is null.
EACCES	Access denied by the authority bit of file mode
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
EPERM	The operation is not allowed or the access is rejected.
EBUSY	The operation is rejected according to the file sharing policy.

## fcntl\(\)
```
int fcntl (int fd, int cmd, ... )
```
**Description:**
Manipulates a specified file descriptor.
**Parameters:**

Name	Description
fd	Indicates the file descriptor.
cmd	Indicates the command used to manipulate the file descriptor.

cmd	Description
F_DUPFD	Copy a new file descriptor (fd is a file).
F_GETFL	Obtain the status of the file specified by fd. (fd is a file or sockets are available.)
F_SETFL	Set the file descriptor status. (fd is a file or sockets are available.)

**Returns:**
Returns the value depending on **cmd** if the operation is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EAGAIN	The operation is prohibited.
EBADF	fd is an invalid file descriptor.
EFAULT	Beyond the accessible address space.
EINVAL	The command specified by cmd cannot be recognized.
ENOLCK	Too many segment locks open, lock table is full, or a remote locking protocol failed.
EPERM	Attempt to clear the O_APPEND flag on a file that has the append-only attribute set.

## fstat\(\)
```
int fstat (int fd, struct [stat](stat.md) * buf )
```
**Description:**
Obtains file status information.
**Parameters:**

Name	Description
fd	Indicates the file descriptor.
buf	Indicates the pointer to a stat structure into which file information is placed.

**Returns:**
Returns **0** if file information is obtained successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EBADF	fd is an invalid file descriptor.
EAGAIN	The file list is null.
EINVAL	Invalid parameter.
ENOENT	A component of path does not name an existing file or path is an empty string.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOMEM	Insufficient memory.
ENOSYS	The function is not supported.
EACCES	Search permission is denied on a component of the path prefix.
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
ENOSPC	No available space on the device.
EISDIR	The named file is a directory.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EBUSY	The operation is rejected according to the file sharing policy.
EPROTO	The protocol in NFS is incorrect.
ENODEV	No such device.
EFAULT	Incorrect IP address.

## ftw\(\)
```
int ftw (const char * path, int(*)(const char *file, const struct [stat](stat.md) *sb, int flag) fn, int depth )
```
**Description:**
Traverses a file tree.
This function is used to traverse a file tree for search.
**Parameters:**

Name	Description
path	Indicates the pointer to the file directory to traverse.
fn	Indicates the pointer to the function to be called for the found entry. For the fn function, file identifies the path of the file relative to path, and sb indicates the pointer to the stat structure. flag indicates the flag. The values of flag are as follows:
depth	Indicates the number of files that can be opened during traversal.

value	Description
FTW_F	Regular file
FTW_D	Directory
FTW_DNR	Unreadable directory. Its subdirectories will not be traversed.
FTW_SL	Symbolic link
FTW_NS	The data of the stat structure cannot be obtained. The possible cause is that the permission is incorrect.

**Returns:**
Returns **0** if the tree is traversed; returns the value that is returned by the **fn\(\)** function if the traversal is interrupted; returns **-1** if an error occurs.
## glob\(\)
```
int glob (const char *__restrict pattern, int flags, int(*)(const char *, int) errfunc, [glob_t](glob_t.md) *__restrict pglob )
```
**Description:**
Searches for path names that meet a specified pattern.
**Parameters:**

Name	Description
pattern	Indicates the pattern you want to match.
flags	Indicates the matching mode.
errfunc	Indicates the pointer to the error processing callback function. If errfunc is not a null pointer, errfunc() is called when an error occurs (opendir(), readdir(), or stat() fails) during the search. If the function returns a non-zero value or GLOB_ERR is set, glob() terminates the entire search process.
pglob	Indicates the pointer to the address storing the matched path names.

flags	Description
GLOB_ERR	GLOB_ERR
GLOB_MARK	GLOB_MARK
GLOB_NOSORT	GLOB_NOSORT
GLOB_DOOFFS	GLOB_DOOFFS
GLOB_NOCHECK	GLOB_NOCHECK
GLOB_APPEND	GLOB_APPEND
GLOB_NOESCAPE	GLOB_NOESCAPE
GLOB_PERIOD	GLOB_PERIOD
GLOB_TILDE	GLOB_TILDE
GLOB_TILDE_CHECK	GLOB_TILDE_CHECK

**Returns:**
Returns **0** on successful completion; returns [GLOB\_NOSPACE](FS.md#gab53de39e075e6fb9a11678341772930b) for running out of memory; returns [GLOB\_ABORTED](FS.md#gab5de50cedafa21283878657d05fb2ba8) for a read error; returns [GLOB\_NOMATCH](FS.md#gaed760cf90fd4398067cdb679ebe60312) for no match found.
## globfree\(\)
```
void globfree ([glob_t](glob_t.md) * pglob)
```
**Description:**
Frees allocated memory from a call to **[glob\(\)](FS.md#gae98601409da7fd3c85a9c219e1a9020c)**.
**Parameters:**

Name	Description
pglob	Indicates the pointer to the address of memory dynamically allocated for a glob call.

## ioctl\(\)
```
int ioctl (int fd, int cmd, ... )
```
**Description:**
Manipulates a device.
This function is used to perform specified operations on an input device file descriptor.
**Parameters:**

Name	Description
fd	Indicates the file descriptor of the device (file-related file descriptors are not supported).
cmd	Indicates the operation instruction for the device. You can define it based on the specific device.

**Returns:**
Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EBADF	fd is an invalid file descriptor.
EFAULT	An inaccessible memory area is referenced.
EINVAL	The command request is invalid.
ENOTTY	fd is not associated with a character special device.

## lstat\(\)
```
int lstat (const char *__restrict path, struct [stat](stat.md) *__restrict buf )
```
**Description:**
Obtains file information.
**Parameters:**

Name	Description
path	Indicates the file path.
buf	Indicates the pointer to a stat structure into which file information is placed.

**Returns:**
Returns **0** if file information is obtained successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	Invalid parameter.
ENOENT	A component of path does not name an existing file or path is an empty string.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOMEM	Insufficient memory.
ENOSYS	The function is not supported.
EAGAIN	The file list is null.
EACCES	The permission bit of the file mode does not allow the requested access, or the search permission is denied on the path prefix component.
EEXIST	The file or directory already exists.
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
ENOSPC	No available space on the device.
ENFILE	The number of opened files in the system has reached the maximum.
ENOTEMPTY	The directory is not empty.
EISDIR	The named file is a directory.
ENOTDIR	A component of the path prefix is the name of an existing file. The file is neither a directory nor a symbolic link of a directory.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EBUSY	The operation is rejected according to the file sharing policy.
EPROTO	The protocol in NFS is incorrect.
ENODEV	No such device.
EFAULT	Incorrect IP address.

## mkdir\(\)
```
int mkdir (const char * pathname, mode_t mode )
```
**Description:**
Creates a directory.
**Parameters:**

Name	Description
pathname	Indicates the pointer to the name of the directory to create.
mode	Indicates the directory permission.

**Attention:**
This function can NOT be used in the PROC file system.
**Returns:**
Returns **0** if the directory is created successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	The pathname is a null pointer or an empty string.
EACCES	The permission bit of the file mode does not allow the requested access, or the search permission is denied on the path prefix directory.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOENT	The directory component in the path name does not exist.
EEXIST	The file or directory already exists.
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
ENOSPC	No available space on the device.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EBUSY	The operation is rejected according to the file sharing policy.
ENOSYS	The function is not supported.
EPROTO	The protocol in NFS is incorrect.
EFAULT	Incorrect IP address.

## mkdirat\(\)
```
int mkdirat (int fd, const char * pathname, mode_t mode )
```
**Description:**
Creates a directory.
**Parameters:**

Name	Description
fd	Indicates the file descriptor of the target directory. (Currently, only AT_FDCWD is supported.)
pathname	Indicates the pointer to the name of the directory to create.
mode	Indicates the directory permission.

errno	Description
EINVAL	The pathname is a null pointer or an empty string.
EACCES	The permission bit of the file mode does not allow the requested access, or the search permission is denied on the path prefix directory.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOENT	The directory component in the path name does not exist.
EEXIST	The file or directory already exists.
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
ENOSPC	No available space on the device.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EBUSY	The operation is rejected according to the file sharing policy.
ENOSYS	The function is not supported.
EPROTO	The protocol in NFS is incorrect.
EFAULT	Incorrect IP address.

## mkfifo\(\)
```
int mkfifo (const char * name, mode_t mode )
```
**Description:**
Creates a named pipe to implement inter-process communication.
**Parameters:**

Name	Description
name	Indicates the pointer to the name of the pipe to create.
mode	Not supported.

**Attention:**
Permission control is not supported. The number of pipes that can be created is not limited. Pipes can be created only in the **/dev** directory.
**Returns:**
Returns **0** if the pipe is created successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	Invalid input parameter (for example, empty address, file name too long or the file is not in the /dev directory).
EEXIST	The file already exists.
ENOMEM	Insufficient memory.

## mount\(\)
```
int mount (const char * source, const char * target, const char * filesystemtype, unsigned long mountflags, const void * data )
```
**Description:**
Mounts a file system.
Mounts a device \(referenced by a file system name\) to a specified directory.
**Parameters:**

Name	Description
source	Indicates the pointer to the device to mount.
target	Indicates the pointer to the path of the mount point.
filesystemtype	Indicates the pointer to the file system type.
mountflags	Indicates the mounting flag.
data	Indicates the pointer to the mounting data.

**Returns:**
Returns **0** if the mounting is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EACCES	A component of the path was not searchable.
EBUSY	source is already mounted.
EFAULT	One of the pointer parameters points outside the user address space.
EINVAL	source cannot be mounted.
ELOOP	Too many links encountered during path name resolution.
EMFILE	(Non-block device) Virtual device table is full.
ENAMETOOLONG	The path name length is greater than the value of MAXPATHLEN.
ENODEV	No such file system type is configured in the kernel.
ENOENT	A path name is null or has a nonexistent component.
ENOMEM	Insufficient memory.
ENOTBLK	source is not a block device.
ENOTDIR	target or the prefix of source is not a directory.
ENGIO	No such device.
EPERM	No permission.

## nftw\(\)
```
int nftw (const char * path, int(*)(const char *file, const struct [stat](stat.md) *sb, int flag, struct [FTW](FTW.md) *s) fn, int fd_limit, int flags )
```
**Description:**
Traverses a file tree.
This function is used to traverse a file tree. It has a similar effect to [ftw](FS.md#ga8dda75835c2b90f305d96e908dc0f84d) except that it takes an additional parameter **flags**.
**Parameters:**

Name	Description
path	Indicates the pointer to the file directory to traverse.
fn	Indicates the pointer to the function to be called for the found entry. For the fn function, file identifies the path of the file relative to path, and sb indicates the pointer to the stat structure. flag indicates the flag. The values of flag are as follows: The fourth argument of fn() is a pointer to a FTW structure.
fd_limit	Indicates the number of files that can be opened during traversal.
flags	Indicates the traversal action. It is a bitwise inclusive-OR of zero or more of the following flags:

value	Description
FTW_F	Regular file
FTW_D	Directory
FTW_DNR	Unreadable directory. Its subdirectories will not be traversed.
FTW_SL	Symbolic link
FTW_NS	The data of the stat structure cannot be obtained. The possible cause is that the permission is incorrect.
FTW_DP	Directory. All subdirectories have been traversed.
FTW_SLN	Symbolic link that names a non-existent file

**Returns:**
Returns **0** if the tree is traversed; returns the value that is returned by the **fn\(\)** function if the traversal is interrupted; returns **-1** if an error occurs.
## open\(\)
```
int open (const char * path, int oflags, ... )
```
**Description:**
Opens a file.
**Parameters:**

Name	Description
path	Indicates the pointer to the name of the file to open.
oflags	Indicates the file access mode. Available values are as follows:

oflags	Description
O_RDONLY	Read-only
O_WRONLY	Write-only
O_RDWR	Read and write
O_APPEND	If set, the file offset will be set to the end of the file prior to each write.
O_CREAT	If the file does not exist, it will be created.
O_LARGEFILE	A file exceeding 2 GB can be created.
O_TRUNC	If the file is opened successfully with O_WRONLY or O_RDWR, its length is truncated to 0.
O_EXCL	Used together with O_CREAT. This function fails if the file exists.
O_DIRECTORY	This flag must be added for opening a directory. Otherwise, the directory fails to be opened.

**Attention:**
This function can NOT be used in the PROC file system to create a file. This function is used to open a file. If the file does not exist, this function creates a file and opens it.
**Returns:**
Returns the file descriptor if the file is opened successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EACCES	Search permission is denied on a component of the path prefix.
EINVAL	The path name format is invalid.
ENAMETOOLONG	The length of path is greater than the value of NAME_MAX.
ENOENT	The O_CREAT flag is not set and the named file does not exist.
ENXIO	Inode is invalid, not a normal character driver, or not a mount point.
EMFILE	All available file descriptors of the process are opened.
EPERM	The file structure corresponding to the file descriptor cannot be obtained.
EEXIST	O_CREAT and O_EXCL are set.
EIO	A hardware error occurs at the low-level disk I/O layer. As a result, the physical drive cannot work.
EROFS	The named file resides on a read-only file system, and either O_WRONLY, O_RDWR, O_CREAT (if file does not exist), or O_TRUNC is set in the oflags parameter.
ENOSPC	The directory or file system that would contain the new file cannot be expanded, the file does not exist, and O_CREAT is specified.
ENFILE	The number of opened files in the system has reached the maximum.
EISDIR	The named file is a directory, and oflags includes O_WRONLY, O_RDWR, or O_CREAT without O_DIRECTORY.
ENOTDIR	A component of the path prefix names an existing file that is not a directory.
EBUSY	The operation is rejected according to the file sharing policy.
ENODEV	The device does not exist.
ENOTEMPTY	The directory is not empty.
ELOOP	Too many symbolic links are encountered.
EFAULT	The IP address is incorrect.

## opendir\(\)
```
[DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849)* opendir (const char * dirname)
```
**Description:**
Opens a specified directory.
**Parameters:**

Name	Description
dirname	Indicates the pointer to the name of directory to open.

**Returns:**
Returns the pointer to the **DIR** structure representing the directory if it is opened successfully; returns **NULL** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	The dirname is empty.
ENAMETOOLONG	The length of the path name string is longer than the value of NAME_MAX.
ENOENT	The path component does not exist.
ENOMEM	The storage memory is insufficient.
ENOTDIR	dirname is not a directory.

## readdir\(\)
```
struct [dirent](dirent.md)* readdir ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) * dirp)
```
**Description:**
Reads a specified directory.
**Parameters:**

Name	Description
dirp	Indicates the pointer to the directory structure.

**Returns:**
Returns the pointer to the **dirent** structure representing the directory if it is read successfully; returns **NULL** if reaching the end of the directory stream or the directory fails to be read. If the directory fails to be read, the corresponding error code is returned.

errno	Description
EACCES	This feature is not supported by the file system.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOENT	The current position in the directory stream is invalid.
EBADF	dirp is not an opened directory stream.

## readdir\_r\(\)
```
int readdir_r ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) *__restrict dirp, struct [dirent](dirent.md) *__restrict entry, struct [dirent](dirent.md) **__restrict result )
```
**Description:**
Reads a specified directory \(thread-safe version\).
**Parameters:**

Name	Description
dirp	Indicates the pointer to the directory structure.
entry	Indicates the entry read from the dirp stream.
result	Indicates the pointer to the returned buffer.

**Returns:**
Returns **0**. If the directory fails to be read, **errno** is sets to a value in the following table.

errno	Description
EACCES	This feature is not supported by the file system.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOENT	The current position in the directory stream is invalid.
EBADF	dirp is not an opened directory stream.

## rewinddir\(\)
```
void rewinddir ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) * dirp)
```
**Description:**
Resets a directory stream read position.
This function is used to change the current read position of the specified directory stream to the original read position \(that is, the start position after the directory stream is opened by [opendir](FS.md#gad09dd96447776d2bc5d8321e4b499591)\).
**Parameters:**

Name	Description
dirp	Indicates the pointer to the directory stream whose read position needs to be reset.

errno	Description
EBADF	dirp is not an opened directory stream.

## scandir\(\)
```
int scandir (const char * dir, struct [dirent](dirent.md) *** namelist, int(*)(const struct [dirent](dirent.md) *) sel, int(*)(const struct [dirent](dirent.md) **, const struct [dirent](dirent.md) **) compar )
```
**Description:**
Scans directory to find the target entries.
**Parameters:**

Name	Description
dir	Indicates the pointer to the directory to scan.
namelist	Indicates the array storing the directory entries filtered by the function referenced by the sel parameter.
sel	Indicates the filtering condition. You can customize the function referenced by this parameter. Value 0 is returned if the filtering condition is not met; a non-zero value is returned otherwise.
compar	Indicates the pointer to the function for sorting the directory entries.

**Returns:**
Returns the number of entries copied to the **namelist** array if the scanning is successful; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	dir is empty.
ENAMETOOLONG	The length of the path name string is greater than the value of NAME_MAX.
ENOENT	The directory component does not exist.
ENOMEM	The storage memory is insufficient.
ENOTDIR	dir is not a directory.
EACCES	This feature is not supported by the file system.

## seekdir\(\)
```
void seekdir ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) * dirp, long offset )
```
**Description:**
Sets the position of the next [readdir](FS.md#ga58257faf8b13b3f14558613c632b2373) call in the directory stream.
**Parameters:**

Name	Description
dirp	Indicates the pointer to the directory stream in which the position of the next readdir call needs to be set.
offset	Indicates the offset of the position relative to the current position.

## stat\(\)
```
int [stat](stat.md) (const char *__restrict path, struct [stat](stat.md) *__restrict buf )
```
**Description:**
Obtains file information.
**Parameters:**

Name	Description
path	Indicates the file path.
buf	Indicates the pointer to a stat structure into which file information is placed.

**Returns:**
Returns **0** if file information is obtained successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	Invalid parameter.
ENOENT	A component of path does not name an existing file or path is an empty string.
ENAMETOOLONG	The path name length is greater than the value of NAME_MAX.
ENOMEM	Insufficient memory.
ENOSYS	The function is not supported.
EAGAIN	The file list is null.
EACCES	The permission bit of the file mode does not allow the requested access, or the search permission is denied on the path prefix component.
EEXIST	The file or directory already exists.
EIO	An I/O error occurs when data is read from or written to the file system.
EROFS	The physical drive is write-protected.
ENOSPC	No available space on the device.
ENFILE	The number of opened files in the system has reached the maximum.
ENOTEMPTY	The directory is not empty.
EISDIR	The named file is a directory.
ENOTDIR	A component of the path prefix is the name of an existing file. The file is neither a directory nor a symbolic link of a directory.
EPERM	Operation not permitted or access denied because the access is prohibited or the directory is full.
EBUSY	The operation is rejected according to the file sharing policy.
EPROTO	The protocol in NFS is incorrect.
ENODEV	No such device.
EFAULT	Incorrect IP address.

## statfs\(\)
```
int statfs (const char * path, struct statfs * buf )
```
**Description:**
Obtains file system information of a file in a specified path.
**Parameters:**

Name	Description
path	Indicates the pointer to the name of the target file.
buf	Indicates the pointer to a statfs structure that stores the information about the file system.

**Returns:**
Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EACCES	Search permission is denied on a component of the path prefix.
EFAULT	buf or path points to an invalid address.
EINTR	The function call was interrupted by a signal.
EIO	An I/O error occurred while reading from the file system.
ELOOP	Too many symbolic links were found.
ENAMETOOLONG	path is too long.
ENOENT	The file referred to by path does not exist.
ENOMEM	Insufficient memory.
ENOSYS	The operation is not supported.
ENOTDIR	A component of the path prefix of path is not a directory.
EOVERFLOW	Information overflow

## statvfs\(\)
```
int [statvfs](statvfs.md) (const char *__restrict path, struct [statvfs](statvfs.md) *__restrict buf )
```
**Description:**
Obtains the file system information.
**Parameters:**

Name	Description
path	Indicates the pointer to the path name of the file.
buf	Indicates the pointer to the statvfs structure that stores the obtained file system information.

**Returns:**
Returns **0** if the file system information is obtained successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EACCES	Search permission is denied on a component of the path prefix.
EFAULT	buf or path points to an invalid address.
EINTR	This call was interrupted by a signal.
EIO	An I/O error occurred while reading from the file system.
ELOOP	Too many symbolic links were found.
ENAMETOOLONG	path is too long.
ENOENT	The file specified by path does not exist.
ENOMEM	Insufficient memory.
ENOSYS	The file system does not support this call.
ENOTDIR	A component of the path prefix of path is not a directory.
EOVERFLOW	Information overflows.

## telldir\(\)
```
long telldir ([DIR](FS.md#ga0ebe68390948c14bb9d82987adbfc849) * dirp)
```
**Description:**
Obtains the current position in the specified directory stream.
**Parameters:**

Name	Description
dirp	Indicates the pointer to the directory stream.

**Returns:**
Returns the current position in the directory stream if the operation is successful; returns **-1** and sets **errno** to the value in the following table otherwise.

errno	Description
EBADF	drip is not an opened directory stream.

## umask\(\)
```
mode_t umask (mode_t mode)
```
**Description:**
Sets umask for a process.
This function sets the umask of the current process file and returns the previous value of the umask. umask is used to turn off permission bits corresponding to in the **mode** parameter.
**Parameters:**

Name	Description
mode	Used to specify the umask value of a process.

**Returns:**
Returns the previous value of the umask. This function call always succeeds.
## umount\(\)
```
int umount (const char * target)
```
**Description:**
Unmounts a file system.
**Parameters:**

Name	Description
target	Indicates the pointer to the path of the file system to unmount.

**Returns:**
Returns **0** if the file system is unmounted successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EBUSY	target could not be unmounted because it is busy.
EFAULT	target points outside the user address space.
EINVAL	target is not a mount point.
ENAMETOOLONG	The path length is greater than the value of MAXPATHLEN.
ENOENT	A path name is null or has a nonexistent component.
ENOMEM	Insufficient memory.
EPERM	No permission.

## umount2\(\)
```
int umount2 (const char * target, int flags )
```
**Description:**
Unmounts a file system.
This function is used to unmount a file system. Currently, the value of **flags** can only be **0**. In this case, this function is the same as **[umount\(\)](FS.md#ga44634cfa8bcc732c29bcdf5822095422)**.
**Parameters:**

Name	Description
target	Indicates the pointer to the path of the file system to unmount.
flags	Indicates the control flag. (Currently, the value of flags can only be 0. In this case, this function is the same as umount().)

**Returns:**
Returns **0** if the file system is unmounted successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EBUSY	target could not be unmounted because it is busy.
EFAULT	target points outside the user address space.
EINVAL	target is not a mount point.
ENAMETOOLONG	The path length is greater than the value of MAXPATHLEN.
ENOENT	A path name is null or has a nonexistent component.
ENOMEM	Insufficient memory.
EPERM	No permission.
ENOSYS	The function call is not supported. (flags value is not 0.)

## utime\(\)
```
int utime (const char * filename, const struct [utimbuf](utimbuf.md) * times )
```
**Description:**
Sets the access time and modification time of a file.
**Parameters:**

Name	Description
filename	Indicates the pointer to the name of the file whose access time and modification time need to be set.
times	Indicates the pointer to the time to which the access time and modification time are set. If times is a null pointer, then the access time and modification time are set to the current time.

**Returns:**
Returns **0** if the access time and modification time are set successfully; returns **-1** and sets **errno** to a value in the following table otherwise.

errno	Description
EINVAL	filename is null or times is invalid.
ENAMETOOLONG	The length of the component in the path name is greater than the value of NAME_MAX.
ENOENT	Some paths do not exist.
ENOSYS	This function is not supported.
EACCES	The file system is read-only.
ENOMEM	Insufficient memory.
EIO	A hardware error occurs at the underlying disk I/O layer.

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