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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2015-05-11 15:13:56 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2015-05-12 07:07:21 +0200 |
| commit | 77548009f57a74740838bb2b3f4547ececdf0251 (patch) | |
| tree | 4052fde89c6196aa2a6915df069e437bc2e4fade | |
| parent | 9a12dd5031ffb76626e0b8d60beee0637e8b5a6c (diff) | |
| download | man-pages-77548009f57a74740838bb2b3f4547ececdf0251.tar.gz | |
pread.2, read.2, readv.2, sendfile.2, write.2: Clarify that Linux limits transfers to a maximum of 0x7ffff000 bytes
See https://bugs.debian.org/629994 and
https://bugs.debian.org/630029.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
| -rw-r--r-- | man2/pread.2 | 6 | ||||
| -rw-r--r-- | man2/read.2 | 10 | ||||
| -rw-r--r-- | man2/readv.2 | 7 | ||||
| -rw-r--r-- | man2/sendfile.2 | 7 | ||||
| -rw-r--r-- | man2/write.2 | 12 |
5 files changed, 42 insertions, 0 deletions
diff --git a/man2/pread.2 b/man2/pread.2 index de1e951b3d..c7a7fdd77d 100644 --- a/man2/pread.2 +++ b/man2/pread.2 @@ -85,6 +85,12 @@ and .BR pwrite () returns the number of bytes written. +Note that is not an error for a successful call to transfer fewer bytes +than requested (see +.BR read (2) +and +.BR write (2)). + On error, \-1 is returned and .I errno is set to indicate the cause of the error. diff --git a/man2/read.2 b/man2/read.2 index 62d7d8b497..c581f72a9c 100644 --- a/man2/read.2 +++ b/man2/read.2 @@ -87,6 +87,8 @@ available right now (maybe because we were close to end-of-file, or because we are reading from a pipe, or from a terminal), or because .BR read () was interrupted by a signal. +See also NOTES. + On error, \-1 is returned, and .I errno is set appropriately. @@ -178,6 +180,14 @@ or to return the number of bytes already read. .SH CONFORMING TO SVr4, 4.3BSD, POSIX.1-2001. .SH NOTES +On Linux, +.BR read () +(and similar system calls) will transfer at most +0x7ffff000 (2,147,479,552) bytes, +returning the number of bytes actually transferred. +.\" commit e28cc71572da38a5a12c1cfe4d7032017adccf69 +(This is true on both 32-bit and 64-bit systems.) + On NFS filesystems, reading small amounts of data will update the timestamp only the first time, subsequent calls may not do so. This is caused diff --git a/man2/readv.2 b/man2/readv.2 index 3cc0813d48..3cf0c2f76c 100644 --- a/man2/readv.2 +++ b/man2/readv.2 @@ -184,6 +184,13 @@ return the number of bytes read; and .BR pwritev () return the number of bytes written. + +Note that is not an error for a successful call to transfer fewer bytes +than requested (see +.BR read (2) +and +.BR write (2)). + On error, \-1 is returned, and \fIerrno\fP is set appropriately. .SH ERRORS The errors are as given for diff --git a/man2/sendfile.2 b/man2/sendfile.2 index 972564c7c2..ef9ba6ce7a 100644 --- a/man2/sendfile.2 +++ b/man2/sendfile.2 @@ -113,6 +113,7 @@ Note that a successful call to .BR sendfile () may write fewer bytes than requested; the caller should be prepared to retry the call if there were unsent bytes. +See also NOTES. On error, \-1 is returned, and .I errno @@ -166,6 +167,12 @@ Other UNIX systems implement with different semantics and prototypes. It should not be used in portable programs. .SH NOTES +.BR sendfile () +will transfer at most 0x7ffff000 (2,147,479,552) bytes, +returning the number of bytes actually transferred. +.\" commit e28cc71572da38a5a12c1cfe4d7032017adccf69 +(This is true on both 32-bit and 64-bit systems.) + If you plan to use .BR sendfile () for sending files to a TCP socket, but need diff --git a/man2/write.2 b/man2/write.2 index 90ef9b5994..3e8c363ab9 100644 --- a/man2/write.2 +++ b/man2/write.2 @@ -89,6 +89,10 @@ Note that not all filesystems are POSIX conforming. .SH RETURN VALUE On success, the number of bytes written is returned (zero indicates nothing was written). +It is not an error if this number is smaller than the number of bytes +requested; this may happen for example because the disk device was filled. +See also NOTES. + On error, \-1 is returned, and \fIerrno\fP is set appropriately. @@ -217,6 +221,14 @@ then the call fails with the error .BR EINTR ; if it is interrupted after at least one byte has been written, the call succeeds, and returns the number of bytes written. + +On Linux, +.BR read () +(and similar system calls) will transfer at most +0x7ffff000 (2,147,479,552) bytes, +returning the number of bytes actually transferred. +.\" commit e28cc71572da38a5a12c1cfe4d7032017adccf69 +(This is true on both 32-bit and 64-bit systems.) .SH BUGS According to POSIX.1-2008/SUSv4 Section XSI 2.9.7 ("Thread Interactions with Regular File Operations"): |