diff options
Diffstat (limited to 'man2/sendfile.2')
| -rw-r--r-- | man2/sendfile.2 | 41 |
1 files changed, 25 insertions, 16 deletions
diff --git a/man2/sendfile.2 b/man2/sendfile.2 index d9c3451..e013fa6 100644 --- a/man2/sendfile.2 +++ b/man2/sendfile.2 @@ -11,7 +11,7 @@ .\" .\" 2005-03-31 Martin Pool <mbp@sourcefrog.net> mmap() improvements .\" -.TH sendfile 2 2023-07-15 "Linux man-pages 6.05.01" +.TH sendfile 2 2023-12-21 "Linux man-pages 6.7" .SH NAME sendfile \- transfer data between file descriptors .SH LIBRARY @@ -20,7 +20,7 @@ Standard C library .SH SYNOPSIS .nf .B #include <sys/sendfile.h> -.PP +.P .BI "ssize_t sendfile(int" " out_fd" ", int" " in_fd" ", \ off_t *_Nullable " offset , .BI " size_t" " count" ); @@ -48,12 +48,12 @@ is more efficient than the combination of and .BR write (2), which would require transferring data to and from user space. -.PP +.P .I in_fd should be a file descriptor opened for reading and .I out_fd should be a descriptor opened for writing. -.PP +.P If .I offset is not NULL, then it points @@ -74,29 +74,38 @@ does not modify the file offset of otherwise the file offset is adjusted to reflect the number of bytes read from .IR in_fd . -.PP +.P If .I offset is NULL, then data will be read from .I in_fd starting at the file offset, and the file offset will be updated by the call. -.PP +.P .I count is the number of bytes to copy between the file descriptors. -.PP +.P The .I in_fd argument must correspond to a file which supports .BR mmap (2)-like operations (i.e., it cannot be a socket). -.PP +Except since Linux 5.12 +.\" commit b964bf53e540262f2d12672b3cca10842c0172e7 +and if +.I out_fd +is a pipe, in which case +.BR sendfile () +desugars to a +.BR splice (2) +and its restrictions apply. +.P Before Linux 2.6.33, .I out_fd must refer to a socket. Since Linux 2.6.33 it can be any file. -If it is a regular file, then +If it's seekable, then .BR sendfile () changes the file offset appropriately. .SH RETURN VALUE @@ -108,7 +117,7 @@ Note that a successful call to may write fewer bytes than requested; the caller should be prepared to retry the call if there were unsent bytes. See also NOTES. -.PP +.P On error, \-1 is returned, and .I errno is set to indicate the error. @@ -169,13 +178,13 @@ None. .SH HISTORY Linux 2.2, glibc 2.1. -.PP +.P In Linux 2.4 and earlier, .I out_fd could also refer to a regular file; this possibility went away in the Linux 2.6.x kernel series, but was restored in Linux 2.6.33. -.PP +.P The original Linux .BR sendfile () system call was not designed to handle large file offsets. @@ -193,7 +202,7 @@ 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.) -.PP +.P If you plan to use .BR sendfile () for sending files to a TCP socket, but need @@ -203,7 +212,7 @@ it useful to employ the option, described in .BR tcp (7), to minimize the number of packets and to tune performance. -.PP +.P Applications may wish to fall back to .BR read (2) and @@ -214,7 +223,7 @@ fails with .B EINVAL or .BR ENOSYS . -.PP +.P If .I out_fd refers to a socket or pipe with zero-copy support, callers must ensure the @@ -223,7 +232,7 @@ transferred portions of the file referred to by remain unmodified until the reader on the other end of .I out_fd has consumed the transferred data. -.PP +.P The Linux-specific .BR splice (2) call supports transferring data between arbitrary file descriptors |