.\" Copyright (C) 2014, Heinrich Schuchardt .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of .\" this manual under the conditions for verbatim copying, provided that .\" the entire resulting derived work is distributed under the terms of .\" a permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume .\" no responsibility for errors or omissions, or for damages resulting .\" from the use of the information contained herein. The author(s) may .\" not have taken the same level of care in the production of this .\" manual, which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .TH IOCTL-FAT 2 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME ioctl_fat \- manipulating the FAT filesystem .SH SYNOPSIS .nf .B #include .B #include .PP .BI "int ioctl(int " fd ", FAT_IOCTL_GET_ATTRIBUTES, uint32_t *" attr ); .BI "int ioctl(int " fd ", FAT_IOCTL_SET_ATTRIBUTES, uint32_t *" attr ); .BI "int ioctl(int " fd ", FAT_IOCTL_GET_VOLUME_ID, uint32_t *" id ); .BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_BOTH, .BI " struct __fat_dirent[2] " entry ); .BI "int ioctl(int " fd ", VFAT_IOCTL_READDIR_SHORT, .BI " struct __fat_dirent[2] " entry ); .fi .SH DESCRIPTION The .BR ioctl (2) system call can be used to read and write metadata of FAT filesystems that are not accessible using other system calls. .SS Reading and setting file attributes Files and directories in the FAT filesystem possess an attribute bit mask that can be read with .B FAT_IOCTL_GET_ATTRIBUTES and written with .BR FAT_IOCTL_SET_ATTRIBUTES . .PP The .I fd argument contains a file descriptor for a file or directory. It is sufficient to create the file descriptor by calling .BR open (2) with the .B O_RDONLY flag. .PP The .I attr argument contains a pointer to a bit mask. The bits of the bit mask are: .TP .B ATTR_RO This bit specifies that the file or directory is read-only. .TP .B ATTR_HIDDEN This bit specifies that the file or directory is hidden. .TP .B ATTR_SYS This bit specifies that the file is a system file. .TP .B ATTR_VOLUME This bit specifies that the file is a volume label. This attribute is read-only. .TP .B ATTR_DIR This bit specifies that this is a directory. This attribute is read-only. .TP .B ATTR_ARCH This bit indicates that this file or directory should be archived. It is set when a file is created or modified. It is reset by an archiving system. .PP The zero value .B ATTR_NONE can be used to indicate that no attribute bit is set. .SS Reading the volume ID FAT filesystems are identified by a volume ID. The volume ID can be read with .BR FAT_IOCTL_GET_VOLUME_ID . .PP The .I fd argument can be a file descriptor for any file or directory of the filesystem. It is sufficient to create the file descriptor by calling .BR open (2) with the .B O_RDONLY flag. .PP The .I id argument is a pointer to the field that will be filled with the volume ID. Typically the volume ID is displayed to the user as a group of two 16-bit fields: .PP .in +4n .EX printf("Volume ID %04x-%04x\\n", id >> 16, id & 0xFFFF); .EE .in .SS Reading short file names of a directory A file or directory on a FAT filesystem always has a short filename consisting of up to 8 capital letters, optionally followed by a period and up to 3 capital letters for the file extension. If the actual filename does not fit into this scheme, it is stored as a long filename of up to 255 UTF-16 characters. .PP The short filenames in a directory can be read with .BR VFAT_IOCTL_READDIR_SHORT . .B VFAT_IOCTL_READDIR_BOTH reads both the short and the long filenames. .PP The .I fd argument must be a file descriptor for a directory. It is sufficient to create the file descriptor by calling .BR open (2) with the .B O_RDONLY flag. The file descriptor can be used only once to iterate over the directory entries by calling .BR ioctl (2) repeatedly. .PP The .I entry argument is a two-element array of the following structures: .PP .in +4n .EX struct __fat_dirent { long d_ino; __kernel_off_t d_off; uint32_t short d_reclen; char d_name[256]; }; .EE .in .PP The first entry in the array is for the short filename. The second entry is for the long filename. .PP The .I d_ino and .I d_off fields are filled only for long filenames. The .I d_ino field holds the inode number of the directory. The .I d_off field holds the offset of the file entry in the directory. As these values are not available for short filenames, the user code should simply ignore them. .PP The field .I d_reclen contains the length of the filename in the field .IR d_name . To keep backward compatibility, a length of 0 for the short filename signals that the end of the directory has been reached. However, the preferred method for detecting the end of the directory is to test the .BR ioctl (2) return value. If no long filename exists, field .I d_reclen is set to 0 and .I d_name is a character string of length 0 for the long filename. .SH RETURN VALUE On error, \-1 is returned, and .I errno is set to indicate the error. .PP For .B VFAT_IOCTL_READDIR_BOTH and .B VFAT_IOCTL_READDIR_SHORT a return value of 1 signals that a new directory entry has been read and a return value of 0 signals that the end of the directory has been reached. .SH ERRORS .TP .B ENOENT This error is returned by .B VFAT_IOCTL_READDIR_BOTH and .B VFAT_IOCTL_READDIR_SHORT if the file descriptor .I fd refers to a removed, but still open directory. .TP .B ENOTDIR This error is returned by .B VFAT_IOCTL_READDIR_BOTH and .B VFAT_IOCTL_READDIR_SHORT if the file descriptor .I fd does not refer to a directory. .TP .B ENOTTY The file descriptor .I fd does not refer to an object in a FAT filesystem. .PP For further error values, see .BR ioctl (2). .SH VERSIONS .BR VFAT_IOCTL_READDIR_BOTH and .B VFAT_IOCTL_READDIR_SHORT first appeared in Linux 2.0. .PP .BR FAT_IOCTL_GET_ATTRIBUTES and .BR FAT_IOCTL_SET_ATTRIBUTES first appeared .\" just before we got Git history in Linux 2.6.12. .PP .B FAT_IOCTL_GET_VOLUME_ID was introduced in version 3.11 .\" commit 6e5b93ee55d401f1619092fb675b57c28c9ed7ec of the Linux kernel. .SH CONFORMING TO This API is Linux-specific. .SH EXAMPLE .SS Toggling the archive flag The following program demonstrates the usage of .BR ioctl (2) to manipulate file attributes. The program reads and displays the archive attribute of a file. After inverting the value of the attribute, the program reads and displays the attribute again. .PP The following was recorded when applying the program for the file .IR /mnt/user/foo : .PP .in +4n .EX # ./toggle_fat_archive_flag /mnt/user/foo Archive flag is set Toggling archive flag Archive flag is not set .EE .in .SS Program source (toggle_fat_archive_flag.c) \& .EX #include #include #include #include #include #include #include /* * Read file attributes of a file on a FAT filesystem. * Output the state of the archive flag. */ static uint32_t readattr(int fd) { uint32_t attr; int ret; ret = ioctl(fd, FAT_IOCTL_GET_ATTRIBUTES, &attr); if (ret == \-1) { perror("ioctl"); exit(EXIT_FAILURE); } if (attr & ATTR_ARCH) printf("Archive flag is set\\n"); else printf("Archive flag is not set\\n"); return attr; } int main(int argc, char *argv[]) { uint32_t attr; int fd; int ret; if (argc != 2) { printf("Usage: %s FILENAME\\n", argv[0]); exit(EXIT_FAILURE); } fd = open(argv[1], O_RDONLY); if (fd == \-1) { perror("open"); exit(EXIT_FAILURE); } /* * Read and display the FAT file attributes. */ attr = readattr(fd); /* * Invert archive attribute. */ printf("Toggling archive flag\\n"); attr ^= ATTR_ARCH; /* * Write the changed FAT file attributes. */ ret = ioctl(fd, FAT_IOCTL_SET_ATTRIBUTES, &attr); if (ret == \-1) { perror("ioctl"); exit(EXIT_FAILURE); } /* * Read and display the FAT file attributes. */ readattr(fd); close(fd); exit(EXIT_SUCCESS); } .EE .\" .SS Reading the volume ID The following program demonstrates the use of .BR ioctl (2) to display the volume ID of a FAT filesystem. .PP The following output was recorded when applying the program for directory .IR /mnt/user : .PP .in +4n .EX $ ./display_fat_volume_id /mnt/user Volume ID 6443-6241 .EE .in .SS Program source (display_fat_volume_id.c) \& .EX #include #include #include #include #include #include #include int main(int argc, char *argv[]) { uint32_t id; int fd; int ret; if (argc != 2) { printf("Usage: %s FILENAME\\n", argv[0]); exit(EXIT_FAILURE); } fd = open(argv[1], O_RDONLY); if (fd == \-1) { perror("open"); exit(EXIT_FAILURE); } /* * Read volume ID. */ ret = ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &id); if (ret == \-1) { perror("ioctl"); exit(EXIT_FAILURE); } /* * Format the output as two groups of 16 bits each. */ printf("Volume ID %04x\-%04x\\n", id >> 16, id & 0xFFFF); close(fd); exit(EXIT_SUCCESS); } .EE .\" .SS Listing a directory The following program demonstrates the use of .BR ioctl (2) to list a directory. .PP The following was recorded when applying the program to the directory .IR /mnt/user : .PP .in +4n .EX $ \fB./fat_dir /mnt/user\fP \[char46] -> '' \[char46]. -> '' ALONGF~1.TXT -> 'a long filename.txt' UPPER.TXT -> '' LOWER.TXT -> 'lower.txt' .EE .in .\" .SS Program source .in +4n .EX #include #include #include #include #include #include int main(int argc, char *argv[]) { struct __fat_dirent entry[2]; int fd; int ret; if (argc != 2) { printf("Usage: %s DIRECTORY\\n", argv[0]); exit(EXIT_FAILURE); } /* * Open file descriptor for the directory. */ fd = open(argv[1], O_RDONLY | O_DIRECTORY); if (fd == \-1) { perror("open"); exit(EXIT_FAILURE); } for (;;) { /* * Read next directory entry. */ ret = ioctl( fd, VFAT_IOCTL_READDIR_BOTH, entry); /* * If an error occurs, the return value is \-1. * If the end of the directory list has been reached, * the return value is 0. * For backward compatibility the end of the directory * list is also signaled by d_reclen == 0. */ if (ret < 1) break; /* * Write both the short name and the long name. */ printf("%s \-> '%s'\\n", entry[0].d_name, entry[1].d_name); } if (ret == \-1) { perror("VFAT_IOCTL_READDIR_BOTH"); exit(EXIT_FAILURE); } /* * Close the file descriptor. */ close(fd); exit(EXIT_SUCCESS); } .EE .in .SH SEE ALSO .BR ioctl (2) .SH COLOPHON This page is part of release 4.16 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.