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Questions and Answers
The file with holes consumes only ______ disk blocks.
The file with holes consumes only ______ disk blocks.
8
The file without holes consumes ______ disk blocks.
The file without holes consumes ______ disk blocks.
20
The size of the offset address that lseek uses is represented by a ______.
The size of the offset address that lseek uses is represented by a ______.
off_t
Most platforms provide one set of interfaces that uses ______-bit file offsets.
Most platforms provide one set of interfaces that uses ______-bit file offsets.
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The Single UNIX Specification allows applications to determine supported environments through the ______ function.
The Single UNIX Specification allows applications to determine supported environments through the ______ function.
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The ______ compiler requires the use of the getconf command to map data size models.
The ______ compiler requires the use of the getconf command to map data size models.
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To enable 64-bit offsets, applications can set the ______ constant to 64.
To enable 64-bit offsets, applications can set the ______ constant to 64.
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Different flags and libraries might be needed, depending on the supported ______.
Different flags and libraries might be needed, depending on the supported ______.
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When interrupted by a signal and a partial amount of data has already been ______.
When interrupted by a signal and a partial amount of data has already been ______.
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The classic definition of the read function includes the prototype 'int read(int fd, char *buf, unsigned ______)'.
The classic definition of the read function includes the prototype 'int read(int fd, char *buf, unsigned ______)'.
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POSIX.1 changed the prototype for the read function from char * to ______ *.
POSIX.1 changed the prototype for the read function from char * to ______ *.
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The return value of the read function is required to be of type ______.
The return value of the read function is required to be of type ______.
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Data is written to an open file with the ______ function.
Data is written to an open file with the ______ function.
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The write function has a prototype that includes 'ssize_t write(int fd, const void *buf, size_t ______)'.
The write function has a prototype that includes 'ssize_t write(int fd, const void *buf, size_t ______)'.
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The return value of a successful write operation is usually equal to the ______ argument.
The return value of a successful write operation is usually equal to the ______ argument.
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If the O_APPEND option was specified when the file was opened, the file's offset is set to the current ______ of file before each write operation.
If the O_APPEND option was specified when the file was opened, the file's offset is set to the current ______ of file before each write operation.
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Setting FILE_OFFSET_BITS to 32 enables 32-bit file offsets.
Setting FILE_OFFSET_BITS to 32 enables 32-bit file offsets.
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The off_t data type is typically a 64-bit signed integer if defined appropriately.
The off_t data type is typically a 64-bit signed integer if defined appropriately.
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Even when enabling 64-bit file offsets, creating a file larger than 2 GB depends on the file system.
Even when enabling 64-bit file offsets, creating a file larger than 2 GB depends on the file system.
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The read function is used to read data from an open file.
The read function is used to read data from an open file.
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If the end of file is encountered, read returns 0.
If the end of file is encountered, read returns 0.
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Reading from a terminal device normally retrieves up to one line at a time.
Reading from a terminal device normally retrieves up to one line at a time.
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Buffering within the network may cause less than the requested amount to be returned.
Buffering within the network may cause less than the requested amount to be returned.
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When reading from a pipe or FIFO, read will return only what is available.
When reading from a pipe or FIFO, read will return only what is available.
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Set the file descriptor flags for fd. The new flag value is set from the third argument taken as an ______.
Set the file descriptor flags for fd. The new flag value is set from the third argument taken as an ______.
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The file status flags can be returned for fd by using the F_GETFL function, which describes the file status flags when we used the ______ function.
The file status flags can be returned for fd by using the F_GETFL function, which describes the file status flags when we used the ______ function.
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The access-mode flags O_RDONLY, O_WRONLY, O_RDWR, O_EXEC, and O_SEARCH are mutually ______.
The access-mode flags O_RDONLY, O_WRONLY, O_RDWR, O_EXEC, and O_SEARCH are mutually ______.
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First, we must use the O_ACCMODE mask to obtain the access-mode bits before comparing them against any of the five ______.
First, we must use the O_ACCMODE mask to obtain the access-mode bits before comparing them against any of the five ______.
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Set the file status flags to the value of the third argument by using the ______ function.
Set the file status flags to the value of the third argument by using the ______ function.
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The SIGIO and SIGURG signals can be received by a process ID or process group ID by using the F_______ function.
The SIGIO and SIGURG signals can be received by a process ID or process group ID by using the F_______ function.
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A positive argument in F_SETOWN specifies a process ID, whereas a negative argument implies a process ______ ID.
A positive argument in F_SETOWN specifies a process ID, whereas a negative argument implies a process ______ ID.
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The return value from fcntl depends on the command, with special return values for F_DUPFD, F_GETFD, F_GETFL, and F_GET______.
The return value from fcntl depends on the command, with special return values for F_DUPFD, F_GETFD, F_GETFL, and F_GET______.
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Synchronous writes are far more expensive than _____ writes.
Synchronous writes are far more expensive than _____ writes.
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The performance of each alternative will depend on many factors, including the underlying operating system implementation and the speed of the _____ drive.
The performance of each alternative will depend on many factors, including the underlying operating system implementation and the speed of the _____ drive.
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The _____ function has always been the catchall for I/O operations.
The _____ function has always been the catchall for I/O operations.
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The performance of fsync and fdatasync can be influenced by the type of _____ system.
The performance of fsync and fdatasync can be influenced by the type of _____ system.
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With the fcntl function, we can modify the properties of a descriptor while knowing only the _____ for the open file.
With the fcntl function, we can modify the properties of a descriptor while knowing only the _____ for the open file.
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The ioctl function was included in the Single UNIX Specification only as an extension for dealing with ______ devices.
The ioctl function was included in the Single UNIX Specification only as an extension for dealing with ______ devices.
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The second argument of the ioctl function is declared as an ______ long in FreeBSD 8.0 and Mac OS X 10.6.8.
The second argument of the ioctl function is declared as an ______ long in FreeBSD 8.0 and Mac OS X 10.6.8.
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Each device driver can define its own set of ______ commands.
Each device driver can define its own set of ______ commands.
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The common FreeBSD ioctl operations include functions for handling ______ tape operations.
The common FreeBSD ioctl operations include functions for handling ______ tape operations.
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The easiest way to handle mag tape devices has always been to access their operations using ______.
The easiest way to handle mag tape devices has always been to access their operations using ______.
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The generic ioctl commands are supported in various categories of ______ devices.
The generic ioctl commands are supported in various categories of ______ devices.
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For terminal I/O operations, specific ioctl commands require ______ header.
For terminal I/O operations, specific ioctl commands require ______ header.
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The return value of the ioctl function is --1 on error, something else if ______.
The return value of the ioctl function is --1 on error, something else if ______.
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Study Notes
3.1 Introduction
- Unix file I/O functions include open, read, write, Iseek, and close
- Unbuffered I/O involves system calls in the kernel for each read/write
- Atomic operations are important for resource sharing among processes
- File descriptors are non-negative integers representing open files
- Descriptors 0, 1, and 2 are typically associated with standard input, output, and error, respectively. This is a convention, not a kernel feature.
3.2 File Descriptors
- Kernel uses file descriptors to refer to open files
- Opening or creating a file returns a file descriptor to the process
- Reading or writing a file is done using the returned file descriptor
- Standard input (0), output (1), and error (2) are common shell associations
3.3 open and openat Functions
- Files are opened or created using open or openat
- The path parameter is the file name
- The oflag argument uses constants from the fcntl.h header to specify options
- Open for reading only (O_RDONLY)
- Open for writing only (O_WRONLY)
- Open for reading and writing (O_RDWR)
- Open for execute only (O_EXEC)
- Append to the end of file (O_APPEND)
- Create the file if it doesn't exist (O_CREAT)
- Generate an error if the path doesn't refer to a directory (O_DIRECTORY)
- Generate an error if the file already exists (O_EXCL)
- Do not allocate the device as the controlling terminal (O_NOCTTY)
3.4 creat Function
- Creates a new file (equivalent to open with O_WRONLY | O_CREAT | O_TRUNC)
3.5 close Function
- Closes an open file
- Returns 0 if successful, otherwise -1
3.6 Iseek Function
- Every open file has a current file offset
- Iseek changes the file offset
- SEEK_SET: Sets the offset to the given value from the beginning of the file
- SEEK_CUR: Sets the offset to the current offset plus the given value
- SEEK_END: Sets the offset to the end-of-file offset plus the given value
3.7 read Function
- Reads data from an open file
- Returns the number of bytes read (or 0 if end of file, or -1 on error)
3.8 write Function
- Writes data to an open file
- Returns the number of bytes written (or -1 if error)
- The offset advances by the number of bytes written for regular files
- O_APPEND sets the offset to the end-of-file before each write operation
3.9 I/O Efficiency
- Program examples illustrate file copying using read and write functions
3.10 File Sharing
- Kernel data structures for open files include process table entry, file table entry, and v-node
3.11 Atomic Operations
- Appending to files can be problematic if not handled correctly if multiple processes access the file
- The O_APPEND option when opening for writing ensures that the write is performed atomically
3.12 dup and dup2 Functions
- dup creates a new file descriptor that refers to the existing file descriptors
- dup2 creates a new file descriptor, replacing the existing file descriptor, if it exists
3.13 sync, fsync, and fdatasync Functions
- sync(void): queues write operations but doesn't wait
- fsync(int fd): waits for writes to complete
- fdatasync(int fd): waits for data to be written to disk, but not necessarily the file attributes
3.14 fcntl Function
- Changes the properties of an open file by setting or getting file descriptor flags or file status flags
3.15 ioctl Function
- Provides access to various I/O operations for devices
-
ioctl(int fd, int request, ...)
3.16 /dev/fd
-
/dev/fdis a directory containing symbolic links to open files; useful for redirection mechanisms
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Description
This quiz covers the fundamental concepts of Unix file I/O operations, including functions such as open, read, and write. It also discusses the significance of file descriptors, standard input/output/error, and atomic operations in process resource sharing. Test your understanding of how files are managed in the Unix operating system!
