4.23. DebugFS interface

The optional DebugFS interface is accessed through a Vendor specific EL3 service. Refer to the component documentation for details.

String parameters are passed through a shared buffer using a specific union:

union debugfs_parms {
    struct {
        char fname[MAX_PATH_LEN];
    } open;

    struct mount {
        char srv[MAX_PATH_LEN];
        char where[MAX_PATH_LEN];
        char spec[MAX_PATH_LEN];
    } mount;

    struct {
        char path[MAX_PATH_LEN];
        dir_t dir;
    } stat;

    struct {
        char oldpath[MAX_PATH_LEN];
        char newpath[MAX_PATH_LEN];
    } bind;
};

Format of the dir_t structure as such:

typedef struct {
    char            name[NAMELEN];
    long            length;
    unsigned char   mode;
    unsigned char   index;
    unsigned char   dev;
    qid_t           qid;
} dir_t;
  • Identifiers

SMC_OK

0

SMC_UNK

-1

DEBUGFS_E_INVALID_PARAMS

-2

MOUNT

0

CREATE

1

OPEN

2

CLOSE

3

READ

4

WRITE

5

SEEK

6

BIND

7

STAT

8

INIT

10

VERSION

11

4.23.1. MOUNT

4.23.1.1. Description

This operation mounts a blob of data pointed to by path stored in src, at filesystem location pointed to by path stored in where, using driver pointed to by path in spec.

4.23.1.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

MOUNT

4.23.1.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if mount operation failed

4.23.2. OPEN

4.23.2.1. Description

This operation opens the file path pointed to by fname.

4.23.2.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

OPEN

uint32_t

mode

mode can be one of:

enum mode {
    O_READ   = 1 << 0,
    O_WRITE  = 1 << 1,
    O_RDWR   = 1 << 2,
    O_BIND   = 1 << 3,
    O_DIR    = 1 << 4,
    O_STAT   = 1 << 5
};

4.23.2.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if open operation failed

uint32_t

w1: file descriptor id on success.

4.23.3. CLOSE

4.23.3.1. Description

This operation closes a file described by a file descriptor obtained by a previous call to OPEN.

4.23.3.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

CLOSE

uint32_t

File descriptor id returned by OPEN

4.23.3.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if close operation failed

4.23.4. READ

4.23.4.1. Description

This operation reads a number of bytes from a file descriptor obtained by a previous call to OPEN.

4.23.4.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

READ

uint32_t

File descriptor id returned by OPEN

uint32_t

Number of bytes to read

4.23.4.3. Return values

On success, the read data is retrieved from the shared buffer after the operation.

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if read operation failed

uint32_t

w1: number of bytes read on success.

4.23.5. SEEK

4.23.5.1. Description

Move file pointer for file described by given file descriptor of given offset related to whence.

4.23.5.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

SEEK

uint32_t

File descriptor id returned by OPEN

sint32_t

offset in the file relative to whence

uint32_t

whence

whence can be one of:

KSEEK_SET

0

KSEEK_CUR

1

KSEEK_END

2

4.23.5.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if seek operation failed

4.23.6. BIND

4.23.6.1. Description

Create a link from oldpath to newpath.

4.23.6.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

BIND

4.23.6.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if bind operation failed

4.23.7. STAT

4.23.7.1. Description

Perform a stat operation on provided file name and returns the directory entry statistics into dir.

4.23.7.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

STAT

4.23.7.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if stat operation failed

4.23.8. INIT

4.23.8.1. Description

Initial call to setup the shared exchange buffer. Notice if successful once, subsequent calls fail after a first initialization. The caller maps the same page frame in its virtual space and uses this buffer to exchange string parameters with filesystem primitives.

4.23.8.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

INIT

uint64_t

Physical address of the shared buffer.

4.23.8.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if already initialized, or internal error occurred.

4.23.9. VERSION

4.23.9.1. Description

Returns the debugfs interface version if implemented in TF-A.

4.23.9.2. Parameters

uint32_t

FunctionID (0x87000010 / 0xC7000010)

uint32_t

VERSION

4.23.9.3. Return values

int32_t

w0 == SMC_OK on success

w0 == SMC_UNK if interface is not implemented

uint32_t

w1: On success, debugfs interface version, 32 bits value with major version number in upper 16 bits and minor version in lower 16 bits.

  • CREATE(1) and WRITE (5) command identifiers are unimplemented and return SMC_UNK.


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